CN117368648A - Power distribution network single-phase earth fault detection method, system, equipment and storage medium - Google Patents
Power distribution network single-phase earth fault detection method, system, equipment and storage medium Download PDFInfo
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Abstract
The invention discloses a single-phase earth fault detection method, a system, equipment and a storage medium for a power distribution network, which belong to the technical field of power systems.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to a method, a system, equipment and a storage medium for detecting single-phase earth faults of a power distribution network.
Background
The distribution network is a part of the power system directly related to users, and has high requirements on power supply reliability, however, due to long lines, many devices and very frequent faults of the distribution network occur. Most of 35kV and 10kV distribution lines are neutral point ungrounded systems, wherein about 70-80% of the distribution lines are single-phase grounding faults. When single-phase earth faults occur, the system is approximately three-phase symmetrical, and the normal operation of the power system of the power plant is not seriously influenced in a short time. But if such a ground fault is not handled for a long time it may lead to more serious faults such as multiphase faults. Therefore, when a single-phase earth fault occurs, it is necessary to judge the fault occurrence line and position as soon as possible and to process as soon as possible.
In the prior art, various single-phase earth fault detection technologies have been proposed, however, in a complex natural environment, due to the influence of climate condition changes such as temperature, humidity, wind speed, etc., weak fault characteristics of single-phase earth faults in a neutral point ungrounded system of a power distribution network cannot be identified rapidly and accurately in the prior art, and fault identification conditions of the power distribution network and high-level operation of the power distribution network cannot be met with high quality, so that research on a technology capable of accurately analyzing the fault characteristics of the power distribution network is needed, and foundation and support are established for fault protection and effective control of faults.
Disclosure of Invention
The invention provides a single-phase earth fault detection method, a system, equipment and a storage medium for a power distribution network, which are used for solving the problems that the prior art cannot quickly and accurately identify weak fault characteristics of single-phase earth faults in a power distribution network neutral point ungrounded system due to the influence of complex natural environments. According to the invention, simulation software pscad is utilized to perform power system simulation, fault zero sequence current is obtained, and a Variation Modal Decomposition (VMD) method optimized by a gray wolf algorithm is matched to perform identification index extraction of fault characteristics, so that the weak fault characteristic identification speed and accuracy of single-phase earth fault of the power distribution network are improved.
The invention is realized by the following technical scheme:
a method for detecting single-phase earth faults of a power distribution network, the method comprising:
establishing a single-phase grounding fault model of a power distribution network center point ungrounded system, performing model simulation, and outputting fault waveforms;
extracting time domain discretization zero sequence current data from the fault waveform;
performing function fitting on the zero sequence current data, taking the fitted function as an optimization rule of a wolf algorithm, obtaining an improved wolf algorithm, and optimizing VMD decomposition parameters by using the improved wolf algorithm;
performing VMD decomposition on the fault waveform by adopting the optimized parameters to obtain an optimal IMF signal;
analyzing the optimal IMF signals obtained by decomposition, and determining fault identification indexes;
and detecting single-phase grounding faults by using the fault identification indexes.
Aiming at the problem that the weak fault characteristics of single-phase earth faults in a neutral point non-earth system of a power distribution network are difficult to quickly and accurately identify under the influence of natural conditions such as temperature, humidity and wind speed in a complex natural environment, the detection method provided by the invention obtains fault electrical quantity waveforms before and after single-phase earth faults through simulation, and extracts discretized electrical quantity data under a time domain, on the basis, an improved gray wolf algorithm is adopted to optimize VMD decomposition parameters, then VMD decomposition is carried out to obtain optimal IMF components, and analysis is carried out on the IMF components, so that fault identification indexes can be determined, modal aliasing is reduced, IMF component waveforms can be quickly and accurately obtained, and the weak fault characteristic identification speed and accuracy of the single-phase earth faults of the power distribution network are improved.
As a preferred implementation mode, the method of the invention utilizes electromagnetic transient simulation software pscad to carry out single-phase grounding modeling and simulation of a neutral point ungrounded system of a power distribution network, and establishes a transition resistance model considering arc resistance, wherein the transition resistance model is expressed as:
r (t) is the transition resistance of the ground point.
As a preferred embodiment, the present invention uses a plurality of sinusoidal function stacks to perform the function fitting.
In the invention, as a preferred implementation manner, VMD decomposition is carried out on the output fault waveform, in order to obtain an optimal IMF component signal, a punishment coefficient and a grading number are required to be set, an improved gray wolf algorithm is adopted to optimize VMD decomposition parameters, the minimum envelope entropy of the IMF component is selected as an optimal solution wolf group of the gray wolf algorithm, and a mathematical model is as follows:
{α，K}＝arg min{E b1 ，E b2 E b3 …E bl }
wherein a is ij Envelope signal, b, being a sub-model of an energy operator ij Is a ij Normalized result, E bj The method is characterized in that the method is used for expressing packet entropy, alpha is a penalty coefficient, l is the number of nodes, N is the number of grades, and K is the number of IMFs.
As a preferred embodiment, the improved wolf algorithm is obtained by taking the fitted function as an optimization rule of the wolf algorithm, and specifically comprises the following steps:
the modification operation is carried out on the gray wolf algorithm:
f(g)＝k(1-n/N max ) 2
wherein a is max Is the upper limit of wolf group individuals, a min Is the lower limit of wolf group individuals, a i For the position of the ith individual, r is [0,1]Random number between, N is iteration number, N max K is a correction parameter, and f (g) is an optimization rule;
inverting the objective function to serve as the fitness function:
as a preferred embodiment, the invention converts VMD decomposition parameters, namely penalty coefficients and grading numbers, into target positions and solving of target functions, wherein the distances between the individuals surrounding the hunting object and the hunting object are as follows:
the location update formula is:
wherein t represents a time variable,position vector representing prey,/->Representing the gray wolf position vector,>andis [0,1 ]]Random vector of>Is an iterative process vector.
As a preferred embodiment, the VMD parameter optimization process of the present invention specifically includes:
setting data parameters related to a wolf algorithm;
initializing the wolf group parameter values, and carrying out mutation operation treatment on the wolf group individuals to form brand new individual orientations;
searching and surrounding the hunting object by the wolf cluster, and setting an iteration frequency threshold;
calculating the fitness function value of each gray wolf individual, and selecting three wolves with the best fitness;
updating the state and position coordinates of each selected gray wolf individual;
updating the parameter values of the wolf groups, selecting excellent individuals according to a preferred strategy, then performing mutation operation treatment on the selected wolf groups to form a brand new individual azimuth, calculating the fitness function value of each gray wolf individual, and selecting three wolves with the best fitness; updating the state and position coordinates of each selected gray wolf individual;
repeating the previous step until the iteration times reach the threshold value, exiting from updating, outputting the global optimization objective data function value, and finally obtaining the optimal punishment coefficient and the grading number.
In a second aspect, the present invention provides a VMD-based single-phase earth fault detection system for a power distribution network, the system comprising:
the simulation unit is used for establishing a single-phase grounding fault model of the power distribution network center point ungrounded system, carrying out model simulation and outputting fault waveforms;
the feature extraction unit is used for extracting time domain discretization zero sequence current data from the fault waveform;
the parameter optimization unit is used for performing function fitting on the zero-sequence current data, taking the fitted function as an optimization rule of the gray wolf algorithm, obtaining an improved gray wolf algorithm, and optimizing VMD decomposition parameters by using the improved gray wolf algorithm;
the decomposition unit carries out VMD decomposition on the fault waveform by adopting the optimized parameters to obtain an optimal IMF signal;
the signal analysis unit is used for analyzing the obtained optimal IMF signal and determining a fault identification index;
and the identification unit is used for carrying out single-phase grounding fault detection by utilizing the fault identification index.
In a third aspect, the present invention proposes a computer device comprising a memory storing a computer program and a processor implementing the steps of the above-mentioned method of the present invention when said computer program is executed by said processor.
In a fourth aspect, the present invention proposes a computer-readable storage medium, on which a computer program is stored, which computer program, when being executed by a processor, carries out the steps of the above-mentioned method of the invention.
According to the single-phase earth fault identification technology of the power distribution network, fault electrical quantity waveforms before and after faults are obtained through pscad modeling simulation, discretized electrical quantity data in a time domain are extracted, a gray wolf algorithm is adopted to conduct parameter optimization on VMDs on the basis, optimal parameters are selected and then decomposed to obtain IMF component waveforms, and finally fault identification parameters and methods are determined through spectrum analysis and amplitude comparison of the component waveforms.
The invention has the following advantages and beneficial effects:
1. according to the invention, the VMD is optimized by adopting an improved gray wolf algorithm, a more accurate IMF component graph can be obtained through extracting and analyzing the fault waveform, the modal aliasing phenomenon is reduced, and compared with a particle swarm optimization algorithm, the convergence speed is faster, so that the weak fault feature recognition speed and accuracy of the single-phase earth fault of the power distribution network are improved.
2. According to the invention, the time-varying arc resistance of the actual situation is considered, so that the transition resistance of the ground fault is closer to the actual fault situation, and the reliability of single-phase ground fault time variation of the power distribution network is further ensured.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention. In the drawings:
FIG. 1 is a flow chart of a VMD-based single phase earth fault identification method of the present invention;
FIG. 2 is a simplified schematic diagram of a pscad fault line of a single phase earth fault of a neutral ungrounded system;
FIG. 3 is a transition resistance model that accounts for arc time-varying resistance;
FIG. 4 is a zero sequence current waveform of a pscad simulation;
FIG. 5 is a zero sequence current diagram of a single phase earth fault;
FIG. 6 is a flow chart of the gray wolf algorithm;
FIG. 7 is a fault zero sequence current function fitting graph;
FIG. 8 is a graph of IMF curves after VMD decomposition;
FIG. 9 is a kurtosis value histogram for each IMF;
fig. 10 is a spectrum analysis chart of each IMF.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present invention, the present invention will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present invention and the descriptions thereof are for illustrating the present invention only and are not to be construed as limiting the present invention.
Examples:
in a complex natural environment, weak fault characteristics of single-phase earth faults in a neutral point of a power distribution network are difficult to quickly and accurately identify due to the influence of natural conditions such as temperature, humidity and wind speed, and the like.
As shown in fig. 1, the method provided in this embodiment includes the following steps:
and step 1, establishing a single-phase grounding fault model of the power distribution network neutral point ungrounded system, performing model simulation, and outputting fault waveforms.
And 2, extracting time domain discretization zero sequence current data from the fault waveform.
And 3, performing function fitting on the zero sequence current data, using the fitted function as an optimization rule of the wolf algorithm to obtain an improved wolf algorithm, and optimizing VMD decomposition parameters by using the improved wolf algorithm.
And 4, performing VMD decomposition on the fault waveform data by adopting the optimized parameters to obtain an optimal IMF signal.
And 5, analyzing the obtained optimal IMF signals to determine fault identification indexes.
And 6, performing single-phase grounding fault detection by using the fault identification index.
In an optional implementation manner, step 1, single-phase grounding modeling and simulation of a neutral point ungrounded system of a power distribution network are performed by using electromagnetic transient simulation software pscad; meanwhile, under the actual condition, a transition resistance model under the condition that the generated arc causes resistance change is considered, zero sequence current waveform data of a fault line are collected and tidied, and data support is provided for fault feature analysis.
Specifically, a simulation model of a certain actual single-phase earth fault ungrounded system is built in the pscad software, the simplified structure of a fault line simulation model is shown as a figure 2, the simulation model comprises a 10kv transformer substation, a 10kv system in a single bus form is allocated through a Y/Y wiring main transformer, the line type is a pure overhead line, and the neutral point is an ungrounded system. The electrical parameter information of the simulation model is as follows:
and a main transformer: sn=25 mva, f=50 hz, Y/Y wiring.
Overhead line: the height of the wires is 10m, the horizontal conduction interval between the grounding wires is 10m, the height of the lowest wires is 8m, and the interval between the grounding wires is 10m.
Aiming at the actual environment condition of a certain power distribution network and the common ground fault position of the power distribution network, the fixed resistance of a ground medium is set to be 100 omega, and an arc resistance model is expressed as follows:
wherein R is s (t) is the arc resistance after the occurrence of the ground fault, C 0 The capacitor is the equivalent capacitance of the power grid to the ground, and L is the zero-sequence equivalent inductance of the single-phase fault; r is the sum of the line resistance and the transition resistance, and ω is the power frequency angular frequency. T is a time variable, T 1 Is the initial moment of arc, theta is the initial phase angle of waveform with fault, T 0 The parameters a, D, etc. are constants related to the grounded medium.
Setting parameters: c (C) 0 L＝1，T 0 ＝8000，a＝34200，T 1 = 23471, θ=0, d= -13, ω=100pi. The ground resistance is set to R 0 Fixed resistance of =100Ω and transition resistance model taking into account arc resistance. Simulation model construction of the transition resistance model is shown in fig. 3, and can be expressed as follows:
R(t)＝R 0 +R s (t)
the values of the parameters are as follows:
wherein R is 0 For the fixed resistance of the grounding medium, the resistance can be identified as a fixed value after the occurrence of the resistance, R is related to the environment and fault position of the power distribution network s And (t) is an arc resistance after the occurrence of the ground fault, and is determined as a time-varying value in relation to an arc temperature, an arc column gap, and the like after the occurrence of the fault.
Fig. 4 is a waveform diagram of a fault phase of the simulation output, in which a single-phase earth fault occurs at 0.3s, and the fault duration is set to 1 second.
For quantitatively representing zero sequence current, differential equation establishment of transient state equivalent loop of transition resistance is carried out: extracting single-phase grounding fault characteristics according to fault phase waveforms output by simulation, and specifically comprises the following steps:
(1) After the single-phase earth fault of the ungrounded system, the zero sequence current distribution is shown in figure 5, and the three-phase voltages of the power supply are respectivelyAnd->It is assumed that the power system is parametrically symmetric. C (C) 1 、C 2 And C 3 For each feeder line to ground capacitance, neglecting the ground conductance of the line, R (t) is the transition resistance of the grounding point, I f Is the ground fault ground current.
The ideal system has three-phase voltage symmetrical distribution under the normal running condition of the three-phase symmetrical load, zero-sequence current cannot occur in the power distribution network, and the single-phase earth fault is an asymmetrical fault of the power system, so that zero-sequence current can be generated when the single-phase earth fault occurs.
(2) When a single-phase earth fault occurs in a system with a neutral point which is not grounded, the resistance of the current flowing through the fault point is a transition resistance, and a transient equivalent loop of the transition resistance can list the differential equation as follows:
wherein u is R Is the sum of the voltages of the transition resistance and the line resistance; u (u) L Is the voltage of the equivalent inductance of the line, u C And i c The equivalent capacitor voltage and the equivalent capacitor current of the power grid are respectively; c (C) 0 The capacitor is the equivalent capacitance of the power grid to the ground, and L is the zero-sequence equivalent inductance of the single-phase fault; r is the sum of the resistance of the circuit and the resistance of the transition resistor; omega is the power frequency angular frequency, and 100 pi is generally adopted;is the initial phase of the failed phase.
Performing time domain analysis on the formula (3) to obtain transient capacitance current as follows:
wherein I C I is the current i flowing through the fault point c Delta is the decay coefficient of the transient capacitance current:
ω f is the oscillation angular frequency of the transient capacitive current:
as can be seen from equation (2), the main factor affecting the transient characteristics of single-phase earth faults is the earth point transitionResistor R tr (the transition resistance is the transition resistance R (t) represented by the arc resistance model above), the failure initiation phase angleLine parameters R, L, C 0 Etc.
An alternative embodiment performs VMD decomposition on the output fault waveform, and iteratively changes to bandwidth-adjusted limited IMF components to achieve an optimal empirical mode decomposition model. The VMD function does not need to select a base function, but obtains a harmonic signal through frequency spectrum decomposition, so that the sum of bandwidths of all modes is minimum, and an optimal solution is formed. To avoid the problem of modal aliasing, it is limited if(/>I.e., the selected basis function), the decomposition is completed, and K optimal IMF components are finally obtained.
In order to obtain the IMF component of the optimization decomposition, a punishment coefficient and a grading number are required to be set, in this embodiment, the VMD is improved and optimized by adopting a gray wolf algorithm with high convergence speed and high optimizing precision, and the minimum envelope entropy of the IMF is selected as the optimal solution wolf group of the gray wolf algorithm, and the mathematical model is as follows:
{α，K}＝arg min{E b1 ，E b2 ，E b3 …E bl }
wherein a is ij Envelope signal, b, being a sub-model of an energy operator ij Is a ij Normalized result, E bj Representation of package entropyAlpha is a penalty coefficient, l represents the number of nodes, N is a hierarchical number, and K represents the number of IMFs.
In the mathematical operation method, an elite retaining strategy is adopted, the three optimal wolf-crowd first individuals are retained, and the three optimal wolf-crowd first individuals directly step into the next generation, and the target finds the most suitable penalty coefficient and grading number, so { alpha, K } is converted into a target position and target function solving method. The distance between the individual wolf group surrounding the prey and the prey is expressed as follows:
the location update formula is as follows:
wherein t represents a time variable,position vector representing prey,/->Representing the gray wolf position vector,>andis [0,1 ]]Random vector of>Is an iterative process vector (linearly decaying from 2 to 0).
And carrying out function fitting analysis on the extracted fault zero sequence current data through a matlab function fitting tool, wherein the analysis result is shown in figure 7, and the smaller the root mean square error of the function fitting is, the closer the fitted function is to the actual condition. By comparing Root Mean Square Error (RMSE) values, a plurality of sine functions are added to fit, and the fitted function expression is as follows:
wherein a1, b1, c1, a2, b2, c2, a3, b3, c3, a4, b4, c4, a5, b5 and c5 are fitting coefficients. And a1= 0.09822, b1=377, c1= 0.5832, a2=0.0316, b2=1005, c2= 2.946, a3= 0.01901, b3= 251.6, c3= -0.307, a4= 0.01252, b4= 879.7, c4= -2.07, a5= 0.006654, b5=1634, c5=2.368.
The root mean square error is as follows: 0.004388 the root mean square error of the function is very small, so the function fit is used.
The fitted function is used as an optimization rule of the gray wolf algorithm. Carrying out mutation operation on the traditional wolf algorithm, thereby randomly selecting independent individuals in the population, obtaining a new individual according to a certain probability, and using P for the mutation rate m And (3) representing. The method has the advantages that the individuals of the traditional wolf algorithm can be mutated and replaced to form new individuals, so that the population scale is enlarged, and more random positions are obtained. The mutation operation mode is as follows:
wherein a is max Is the upper limit of wolf group individuals, a min Is the lower limit of wolf group individuals, a i Is where the i-th individual is located. r is [0,1 ]]Random number between, N is iteration number, N max Is the maximum number of evolutions. k is a correction parameter, and f (g) is an optimization rule, i.e., f (x) of formula (11).
Since the objective function f (g), i.e., the fitting function f (x), is the minimum envelope entropy for achieving IMF, it is necessary to invert the objective function to use as the fitness function, i.e.:
the adoption of the compiling algorithm can enhance the searching capability of the gray wolf operation, thereby achieving the purpose of selecting the optimal punishment coefficient and the grading number. As shown in fig. 6, the optimization process comprises the following specific steps:
step one: setting the initial parameters N, T, P of the data relating to the wolf algorithm m D, population scale value n=100, maximum iteration number t=200, variation probability value P m =0.02, search dimension d=2;
step two: initializing wolf group parameter values a, C and A, and carrying out mutation operation treatment by adopting a formula (12) according to the individual orientations of the wolf group to form a brand new individual orientation;
step three: searching and surrounding a prey by the wolf group, and setting the iteration times t;
step four: calculating the fitness function of each individual wolf according to the formula (13), and selecting three wolves with the best fitness as the wolves respectively
Step five: updating the state and position coordinates of three gray wolf individuals with the best current adaptability according to the distance expression (8) and the position updating expression (9);
step six: updating parameter values of a, C and A in the operation method, selecting three excellent individuals with the best fitness according to a preferable strategy, selecting individuals with brand new variation according to a formula (12), and calculating a fitness function value according to a formula (13);
step seven: updating selected wolvesIs fit and position of (a);
step eight: and when the maximum iteration times T=200, the operation is stopped, and the global optimization objective data function value is output at the same time, so that the optimal penalty coefficient and the grading number are finally obtained.
The simulation shows that the optimal comprehensive index obtained after the optimization of the algorithm is-0.16744, the gray wolf basically stops after the 100 th iteration, and the optimal parameter { alpha, K } = (605,8) obtained through the iteration is faster than the PSO algorithm in convergence speed. And (3) bringing the iterative data result into the VMD, setting a punishment coefficient alpha=605 and IMF component number K=8 of the VMD, decomposing fault phase zero sequence current to obtain the optimal mode bandwidth minimum sum, and verifying to obtain the improvement of the VMD method decomposition mode aliasing phenomenon.
Analysis of the decomposed IMF components can result in the energy and energy entropy of each IMF component after VMD decomposition as shown in table 1, and IMF components and kurtosis values and spectra thereof as shown in fig. 8-10. Wherein, table 1 is the energy and energy entropy of each IMF component after VMD decomposition, which can exhibit the characteristics of a portion of fault phase zero sequence current.
TABLE 1
The IMF component after VMD decomposition is shown in fig. 8, and as can be seen from the figure, the feature difference of VMD is obvious, and the difference is large. As shown in FIG. 10, the IMF components of the IMF kurtosis values show remarkable characteristics, have certain differences, and particularly, the kurtosis value of the seventh IMF component is far higher than the kurtosis value of other seven IMF components, and can be used as the characteristic display of fault phase zero sequence current. As shown in FIG. 10, the spectrum analysis chart of each IMF is relatively large, the spectrum chart of each IMF3 is approximately 0, the values of IMF1 and IMF2 are relatively large, the function characteristics are relatively obvious, and the zero-sequence current fault characteristics can be shown.
From the above, it can be seen from fig. 8 to 10 that: the kurtosis value of the seventh IMF component can be used as a fault zero sequence current characteristic which can be identified by the fault detection method, the fault characteristic of the single-phase grounding fault of the power distribution network under the condition of an arc time-varying resistor can be accurately expressed, the identification performance of the grounding fault of the power distribution network is obviously improved, and the method has certain superiority.
The embodiment also provides a VMD-based single-phase earth fault detection system for a power distribution network, which comprises:
and the simulation unit is used for establishing a single-phase grounding fault model of the power distribution network neutral point ungrounded system, performing model simulation and outputting fault waveforms.
And the feature extraction unit is used for extracting time domain discretization zero sequence current data from the fault waveform.
And the parameter optimization unit is used for performing function fitting on the zero sequence current data, taking the fitted function as an optimization rule of the gray wolf algorithm, obtaining an improved gray wolf algorithm, and optimizing VMD decomposition parameters by using the improved gray wolf algorithm.
And the decomposition unit is used for performing VMD decomposition on the fault waveform data by utilizing the optimized parameters to obtain an optimal IMF signal.
And the signal analysis unit is used for analyzing the obtained optimal IMF signal and determining a fault identification index.
And the identification unit is used for carrying out single-phase grounding fault detection by utilizing the fault identification index.
The embodiment also provides a computer device for executing the method of the embodiment.
The computer device includes a processor, an internal memory, and a system bus; various device components, including internal memory and processors, are connected to the system bus. A processor is a piece of hardware used to execute computer program instructions by basic arithmetic and logical operations in a computer system. Internal memory is a physical device used to temporarily or permanently store computing programs or data (e.g., program state information). The system bus may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus. The processor and the internal memory may communicate data via a system bus. The internal memory includes a Read Only Memory (ROM) or a flash memory (not shown), and a Random Access Memory (RAM), which generally refers to a main memory loaded with an operating system and computer programs.
Computer devices typically include an external storage device. The external storage device may be selected from a variety of computer readable media, which refers to any available media that can be accessed by a computer device, including both removable and fixed media. For example, computer-readable media includes, but is not limited to, flash memory (micro-SD card), CD-ROM, digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computer device.
The computer device may be logically connected to one or more network terminals in a network environment. The network terminal may be a personal computer, server, router, smart phone, tablet computer, or other public network node. The computer device is connected to a network terminal through a network interface (local area network LAN interface). Local Area Networks (LANs) refer to computer networks of interconnected networks within a limited area, such as a home, school, computer laboratory, or office building using network media. WiFi and twisted pair wired ethernet are the two most common technologies used to construct local area networks.
It should be noted that other computer systems including more or fewer subsystems than computer devices may also be suitable for use with the invention.
As described in detail above, the computer apparatus suitable for the present embodiment can perform the specified operation of the single-phase earth fault detection method. The computer device performs these operations in the form of software instructions that are executed by a processor in a computer-readable medium. The software instructions may be read into memory from a storage device or from another device via a lan interface. The software instructions stored in the memory cause the processor to perform the method of processing group member information described above. Furthermore, the invention may be implemented by means of hardware circuitry or by means of combination of hardware circuitry and software instructions. Thus, implementation of the present embodiments is not limited to any specific combination of hardware circuitry and software.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (10)
1. The utility model provides a distribution network single-phase earth fault detection method which is characterized in that the method comprises the following steps:
establishing a single-phase grounding fault model of a power distribution network center point ungrounded system, performing model simulation, and outputting fault waveforms;
extracting time domain discretization zero sequence current data from the fault waveform;
performing function fitting on the zero sequence current data, taking the fitted function as an optimization rule of a wolf algorithm, obtaining an improved wolf algorithm, and optimizing VMD decomposition parameters by using the improved wolf algorithm;
performing VMD decomposition on the fault waveform by adopting the optimized parameters to obtain an optimal IMF signal;
analyzing the optimal IMF signals obtained by decomposition, and determining fault identification indexes;
and detecting single-phase grounding faults by using the fault identification indexes.
2. The method for detecting the single-phase earth fault of the power distribution network according to claim 1, wherein the method utilizes electromagnetic transient simulation software pscad to perform single-phase earth modeling and simulation of a neutral point ungrounded system of the power distribution network, and simultaneously establishes a transition resistance model considering arc resistance, wherein the transition resistance model is expressed as:
r (t) is the transition resistance of the ground point.
3. A method for single phase earth fault detection of a power distribution network according to claim 1, wherein a plurality of sinusoidal function stacks are employed for function fitting.
4. The method for detecting single-phase earth faults of a power distribution network according to claim 1, wherein the output fault waveform is subjected to VMD decomposition, a penalty coefficient and a grading number are required to be set for obtaining an optimal IMF component signal, an improved wolf algorithm is adopted for optimizing VMD decomposition parameters, and the minimum envelope entropy of the IMF component is selected as an optimal solution wolf group of the wolf algorithm, and a mathematical model is as follows:
{α，K}＝argmin{E b1 ，E b2 E b3 …E bl }
wherein a is ij Envelope signal, b, being a sub-model of an energy operator ij Is a ij Normalized result, E bj The method is characterized in that the method is used for expressing packet entropy, alpha is a penalty coefficient, l is the number of nodes, N is the number of grades, and K is the number of IMFs.
5. The method for detecting single-phase earth faults of a power distribution network according to claim 4, wherein the fitted function is used as an optimization rule of a wolf algorithm to obtain an improved wolf algorithm, and the method specifically comprises the following steps:
the modification operation is carried out on the gray wolf algorithm:
f(g)＝k(1-n/N max ) 2
wherein a is max Is the upper limit of wolf group individuals, a min Is the lower limit of wolf group individuals, a i For the position of the ith individual, r is [0,1]Random number between, N is iteration number, N max K is a correction parameter, and f (g) is an optimization rule;
inverting the objective function to serve as the fitness function:
6. the method for detecting single-phase earth faults of a power distribution network according to claim 5, wherein VMD decomposition parameters, namely penalty factors and grading numbers, are converted into target positions and solving of target functions, and the distances between the individuals surrounding the hunting object and the hunting object are as follows:
the location update formula is:
wherein t represents a time variable,position vector representing prey,/->Representing the gray wolf position vector,>and->Is [0,1 ]]Random vector of>Is an iterative process vector.
7. The method for detecting single-phase earth faults of a power distribution network according to claim 6, wherein the VMD parameter optimization process specifically comprises:
setting data parameters related to a wolf algorithm;
initializing the wolf group parameter values, and carrying out mutation operation treatment on the wolf group individuals to form brand new individual orientations;
searching and surrounding the hunting object by the wolf cluster, and setting an iteration frequency threshold;
calculating the fitness function value of each gray wolf individual, and selecting three wolves with the best fitness;
updating the state and position coordinates of each selected gray wolf individual;
updating the parameter values of the wolf groups, selecting excellent individuals according to a preferred strategy, then performing mutation operation treatment on the selected wolf groups to form a brand new individual azimuth, calculating the fitness function value of each gray wolf individual, and selecting three wolves with the best fitness; updating the state and position coordinates of each selected gray wolf individual;
repeating the previous step until the iteration times reach the threshold value, exiting from updating, outputting the global optimization objective data function value, and finally obtaining the optimal punishment coefficient and the grading number.
8. A VMD-based single-phase earth fault detection system for a power distribution network, the system comprising:
the simulation unit is used for establishing a single-phase grounding fault model of the power distribution network center point ungrounded system, carrying out model simulation and outputting fault waveforms;
the feature extraction unit is used for extracting time domain discretization zero sequence current data from the fault waveform;
the parameter optimization unit is used for performing function fitting on the zero-sequence current data, taking the fitted function as an optimization rule of the gray wolf algorithm, obtaining an improved gray wolf algorithm, and optimizing VMD decomposition parameters by using the improved gray wolf algorithm;
the decomposition unit carries out VMD decomposition on the fault waveform by adopting the optimized parameters to obtain an optimal IMF signal;
the signal analysis unit is used for analyzing the obtained optimal IMF signal and determining a fault identification index;
and the identification unit is used for carrying out single-phase grounding fault detection by utilizing the fault identification index.
9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor implements the steps of the method of any of claims 1-7 when the computer program is executed.
10. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the method according to any of claims 1-7.
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