CN117805554A - Transient line selection method and system for single-phase earth fault of power distribution network ring network - Google Patents
Transient line selection method and system for single-phase earth fault of power distribution network ring network Download PDFInfo
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Abstract
The invention discloses a transient line selection method and a system for single-phase grounding faults of a power distribution network, wherein three-phase currents and three-phase voltages in the running process of a simulation model of the low-current grounding power distribution network are obtained in real time, fault characteristics are extracted, phase comparison line selection is carried out based on the extracted fault characteristics and by combining an improved VMD algorithm and Hilbert transformation, the transient line selection after the single-phase grounding faults of the low-current power distribution network can be realized, and technical support is provided for the single-phase grounding fault research of the low-current grounding system of the power distribution network.
Description
Technical Field
The invention belongs to the technical field of power distribution network fault detection, and particularly relates to a transient line selection method and system for a single-phase earth fault of a power distribution network ring network.
Background
In the current low-voltage distribution network, the neutral point has three connection modes, namely the neutral point is not grounded, is grounded through an arc suppression coil and is grounded through high resistance, and the neutral point is commonly called as a low-current grounding system. According to the fault statistics of the power operation department, single-phase ground faults are most common in a low-current ground system of the power distribution network, and the occurrence rate is highest and exceeds 80% of total faults. In addition, when a single-phase earth fault occurs in the low-current grounding system, the system can continue to operate for 1-2 hours under the fault condition due to the small fault current and fault voltage. Therefore, in order to prevent insulation breakdown of other phases caused by long-term overvoltage, faults develop into interphase faults, power supply is affected, and it is important to rapidly and accurately select lines of faults under the conditions of not interrupting power supply continuity and guaranteeing safety of a power distribution network.
At present, a small-current grounding system line selection method applied in an electric power system is mainly divided into a steady-state component-based line selection method, a transient component-based line selection method and an external injection method, wherein the steady-state component-based line selection methods are based on fault signals of single-phase grounding faults, and most of the small-current grounding system line selection methods are directed against zero sequence components of the system, including a group ratio amplitude phase method, a power frequency reactive power direction method, a negative sequence current method, a fifth harmonic method and the like, and have certain stability and accuracy, but in some systems, steady-state fault characteristics of the small-current grounding system are weaker, and the sensitivity of line selection can be influenced; although the transient component-based line selection method is sensitive, the transient process of the single-phase earth fault of the power distribution network is difficult to accurately grasp due to the short transient process; the external injection method is not universal and practical because of the additional equipment required.
The development of the ring network of the power system is mainly used for improving the reliability and the economy of the power system. In the traditional power system, the reliability of the power system is ensured by unidirectional power supply and standby power supply, but the mode has great defects, such as the problem that the standby power supply cannot ensure 100% of reliability, energy waste and the like. The power supply ring network refers to a power supply mode that a power supply and a load point are connected into a ring shape by a power line. A ring network system refers to an electrical network of a plurality of electrical devices that are joined together to form a ring structure. In this configuration, the power equipment is responsible for connecting, regulating and managing voltage and current, and is capable of providing energy from an isomorphic power system. The annular power supply can improve the power supply reliability, and when any section of line in the annular fails, the failed section is cut off through the switch, so that the power supply to the load point is not influenced; and voltage loss and power loss can be reduced, and the electric energy quality and the power supply economy are improved. But relay protection and operation of the ring power supply are complex.
At present, the research related to the ring network line selection of the power distribution network is relatively less, and the examination and the research of a fault line selection scheme after the single-phase earth fault of the ring network of the power distribution network are urgent problems to be solved.
Disclosure of Invention
Aiming at the problem of insufficient research on single-phase grounding faults of a low-current grounding power distribution network ring network system, the invention provides a transient line selection method and a system aiming at the single-phase grounding faults of the power distribution network ring network.
The invention is realized by the following technical scheme:
a transient line selection method for a single-phase earth fault of a power distribution network ring network, the transient line selection method comprising:
establishing a ring network simulation model of the low-current grounding power distribution network;
recording three-phase current and three-phase voltage of each line in the running process of the looped network simulation model of the low-current grounded power distribution network in real time;
extracting zero sequence current and zero sequence voltage of each line based on three-line current and three-phase voltage of each line;
decomposing the zero sequence current and the zero sequence voltage of each circuit by adopting an improved variation modal decomposition algorithm to obtain corresponding transient values;
and carrying out Hilbert transformation on the transient state quantity of each line, and carrying out line selection by combining a phase comparison line selection method.
The existing line selection technology for the single-phase earth fault of the low-current grounding distribution network ring system has less research, and meanwhile, the existing line selection method based on steady-state analysis is not suitable for the line selection of the single-phase earth fault of the ring network because the single-phase earth fault of the ring network has the characteristics of diversity of fault current flow direction, easy interference of fault characteristics and unstable phase and polarity of the fault characteristics. According to the transient line selection method, three-phase current and three-phase voltage in the running process of the small-current grounding distribution network ring network simulation model are obtained in real time, fault characteristics are extracted, phase comparison line selection is carried out based on the extracted fault characteristics and by combining an improved VMD algorithm and Hilbert transformation, transient line selection after single-phase grounding faults of a small-current distribution network system occur can be achieved, and technical support is provided for single-phase grounding fault research of the small-current grounding system of the distribution network ring network.
As a preferred implementation mode, the method for establishing the ring network simulation model of the low-current grounding distribution network specifically comprises the following steps:
establishing a low-current grounding distribution network ring network model in electromagnetic transient simulation software;
and adding an analog single-phase grounding fault into any line of the established low-current grounding distribution network ring network model.
As a preferred embodiment, the simulated single-phase ground fault of the present invention is controlled by a logic time controlled model that is capable of controlling the time that the simulated single-phase ground fault is initiated and sustained.
As a preferred implementation mode, the zero sequence current extracted by the invention is the sum of three-phase currents multiplied by 1/3; the extracted zero sequence voltage is the sum of three-phase voltages and multiplied by 1/3;
and the zero sequence current and the zero sequence voltage are obtained through the cooperation calculation of an adder and a multiplier.
As a preferred embodiment, the improved variant modal decomposition algorithm of the invention is specifically:
selecting a preset scale in the variation modal decomposition algorithm based on a time-frequency entropy stabilization criterion;
and selecting punishment parameters in the variation modal decomposition algorithm based on a multi-scale sample entropy minimum criterion.
As a preferred embodiment, the method for selecting the preset scale in the variation modal decomposition algorithm based on the time-frequency entropy stability criterion specifically includes:
the components obtained through decomposition of the variation modal decomposition algorithm under different preset scale values are subjected to Hilbert variation to obtain amplitude superposition of the same points of the instantaneous frequency, and a sparse matrix is constructed;
dividing the sparse matrix into equal area areas, and obtaining a time-frequency entropy value;
and determining an optimal preset scale value in the variation modal decomposition algorithm according to the time-frequency entropy value.
As a preferred embodiment, the Hilbert transform for the transient state quantity of each line specifically comprises the following steps:
performing Hilbert transformation on the transient state quantity of each line to generate a complex signal;
the amplitude and phase angle of the complex signal are calculated.
As a preferred embodiment, the present invention provides a method for selecting a line by combining a phase comparison line selection method, comprising:
and determining a fault line according to the phase angles of the lines and combining phase criteria of the selected lines.
As a preferred embodiment, the phase criteria of the present invention are specifically: the zero sequence current phase angle of the fault line is 90 degrees different from that of the normal line.
On the other hand, the invention also provides a transient line selection system aiming at the single-phase earth fault of the power distribution network ring network, which comprises the following steps:
the simulation model building unit is used for building a ring network simulation model of the low-current grounding power distribution network;
the data monitoring unit is used for recording three-phase current and three-phase voltage of each line in the running process of the looped network simulation model of the low-current grounded power distribution network in real time;
the characteristic extraction unit is used for extracting and obtaining zero sequence currents and zero sequence voltages of all the lines based on the three-phase currents and the three-phase voltages of all the lines;
the variation modal decomposition unit adopts an improved variation modal decomposition algorithm to decompose the zero sequence current and the dummy voltage of each line to obtain corresponding transient quantity;
and the transformation line selection unit is used for carrying out Hilbert transformation on the transient state quantity of each line and selecting lines by combining a phase comparison line selection method.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the transient line selection method provided by the invention, three-phase current and three-phase voltage in the running process of the small-current grounding distribution network ring network simulation model are obtained in real time, fault characteristic extraction is carried out, phase comparison line selection is carried out based on the extracted fault characteristic and by combining an improved VMD algorithm and Hilbert transformation, transient line selection after single-phase grounding fault of a small-current distribution network system occurs can be realized, and technical support is provided for single-phase grounding fault research of the small-current grounding system of the distribution network ring network;
2. compared with the conventional VMD algorithm, the improved VMD algorithm combined with Hilbert transformation has higher accuracy and robustness, and is not only suitable for single-phase grounding fault line selection of a power distribution network ring network system, but also suitable for single-phase grounding fault line selection of a common low-current grounding system.
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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 transient line selection method according to an embodiment of the invention.
Fig. 2 is a diagram of a ring network structure of a low-current grounded power distribution network according to an embodiment of the present invention.
Fig. 3 is a schematic block diagram of a transient line selection system according to an embodiment of the present invention.
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:
the existing line selection technology for the single-phase earth fault of the low-current grounding distribution network ring system has less research, and meanwhile, the existing line selection method based on steady-state analysis is not suitable for the line selection of the single-phase earth fault of the ring network because the single-phase earth fault of the ring network has the characteristics of diversity of fault current flow direction, easy interference of fault characteristics and unstable phase and polarity of the fault characteristics. Based on the zero sequence fault characteristics, the transient line selection method for the single-phase earth fault of the power distribution network is provided by the embodiment, and the transient options of the single-phase earth fault of the power distribution network are realized by combining an improved variation modal decomposition algorithm and Hilbert transformation based on the zero sequence fault characteristics.
As shown in fig. 1, the transient line selection method provided in this embodiment specifically includes the following steps:
and step 1, establishing a ring network simulation model of the low-current grounding distribution network.
Specifically, the embodiment establishes a low-voltage-class low-current grounding distribution network ring network model in electromagnetic transient simulation software (e.g., PSCAD): three circuits (20 KM,30KM and 41 KM) consisting of two groups of overhead lines are respectively led out from two power supplies (S1 and S2) with the same voltage levels, the voltage levels of the three circuits are the same, and the circuits are connected with different loads; the two power supplies are respectively used as distributed power supplies to supply power to one of the other power supply leading-out lines to form a ring network, as shown in fig. 2; in any line of the established low-current grounding distribution network ring network model, a simulated single-phase grounding Fault controlled by a logic time control model is added, and the logic time control model can control the starting and lasting time of the single-phase grounding Fault, such as the single-phase grounding Fault added by Fault shown in fig. 2.
And 2, recording three-phase current and three-phase voltage of each circuit in the operation process of the looped network simulation model of the low-current grounded power distribution network in real time.
And 3, extracting the zero sequence current and the zero sequence voltage of each line based on the three-line current and the three-phase voltage of each line because the transient fault characteristics of each line are extracted from the zero sequence components of each line.
Specifically, the zero sequence current is the phasor sum of three-phase current multiplied by 1/3; similarly, the zero sequence voltage is the phasor sum of the three-phase voltages and multiplied by 1/3, the zero sequence current and the zero sequence voltage of each line can be obtained through the cooperation of the adder and the multiplier, and the output element and the waveform display element cooperate with each line zero sequence current and each line zero sequence voltage when the real-time display system operates.
And 4, decomposing the zero sequence current and the zero sequence voltage of each line by adopting an improved Variational Modal Decomposition (VMD) algorithm to obtain corresponding transient values.
Specifically, the looped network single-phase earth fault has the characteristics of fault current flow direction diversity, fault characteristics are easy to interfere, and the phase and polarity of the fault characteristics are unstable. The VMD algorithm can automatically adapt to the local characteristics and changes of the signals and correspondingly adjust according to the scale and frequency characteristics of the signals, so that the VMD algorithm can be better suitable for complex and changeable signals; the VMD algorithm also has orthogonality and energy accumulation, and compared with algorithms such as Empirical Mode Decomposition (EMD) and Local Mean Decomposition (LMD), the method avoids the problems of mutual interference and mutual overlapping possibly existing in the traditional mode decomposition method; the VMD algorithm has strong expandability and flexibility, can be applied to signal analysis of different types, can be combined with other signal processing modes, and has a good analysis effect and a large application range. However, some parameters in the VMD algorithm need to be selected, such as regularization parameters and iteration number. The choice of these parameters is critical to the accuracy and stability of the decomposition result. If the parameters are not properly selected, the result may be not ideal or even not converged; furthermore, VMD algorithms are sensitive to noise of the signal, which introduces random components into the signal that may interfere with modal decomposition of the signal. Therefore, the present embodiment uses an improved VMD algorithm to decompose the zero sequence current and zero sequence voltage for each line.
In order to effectively extract morphological spectrum characteristics of the signals, background components and environmental noise in the signals need to be filtered. In the VMD algorithm, the preset scale number K and the punishment parameter alpha are the most important parameters in the signal decomposition process, wherein the preset scale number K determines the number of decomposed IMF components, and if the K is improperly selected, the phenomenon of under decomposition or over decomposition is extremely easy to generate, so that the problem of modal aliasing is generated; the bandwidth of each IMF component is determined by selecting the penalty parameter alpha, the smaller the penalty parameter alpha is, the larger the bandwidth of the IMF component is, and otherwise, the smaller the bandwidth of each IMF component is. The conventional parameter setting method is a default method, which cannot ensure whether the parameter selection is applicable to all analyzed signals, and an intelligent algorithm can be adopted to optimize related parameters, but the process is complex, the efficiency is low, and the influence of all parameters on the signal reconstruction characteristics is not considered. For this, the present embodiment proposes a method for selecting a penalty parameter α based on a preset scale number K of a time-frequency entropy stability criterion and a multi-scale sample entropy minimum criterion.
The time-frequency distributed signal of the signal effectively describes the energy change condition of different frequencies in the sampling time, is less influenced by noise factors in the signal, and the time-frequency entropy is the quantitative description of the change degree. The IMF components obtained by VMD decomposition are generally distributed from low frequency to high frequency, and if the optimal preset scale number K is obtained, the time-frequency distribution of the IMF components is reasonable; along with the increase of the K value, the time-frequency distribution characteristic has better stability, so that the embodiment superimposes the amplitudes of the same instantaneous frequency points obtained by Hilbert transformation of each IMF component under different K values, constructs a sparse matrix, and divides the sparse matrix into equal area areas, thereby obtaining a time-frequency entropy value and determining the value of K according to the time-frequency entropy value. The multi-scale sample entropy is a multi-scale analysis method based on the sample entropy, and the measurement of multi-scale and nonlinear characteristics is integrated. When calculating the multi-scale sample entropy, carrying out wavelet decomposition on the signal to obtain sub-signals with multiple scales. Then, sample entropy calculation is carried out on each sub-signal, and a plurality of sample entropy values are obtained. And finally, carrying out weighted average on the plurality of sample entropy values to obtain the multi-scale sample entropy. And determining a penalty parameter alpha according to the multi-scale sample entropy minimum criterion and the multi-scale sample entropy value.
VMD decomposes the zero sequence current signal i (t), expressed as:
k is the number of the IMFs of the modal component function;respectively obtaining deviation of an impact function and time t; { H k }、{ω k And the k-th modal component function IMF and the corresponding center frequency after the current signal is decomposed are respectively shown.
Introducing a quadratic penalty parameter alpha and a Lagrangian multiplier lambda (t), wherein the extended Lagrangian expression is as follows:
and adopting an alternate direction multiplier iteration algorithm to update and solve the solution iteratively. The above is the mathematical expression of the VMD algorithm core to find the modal component function of the zero sequence fault component and its corresponding center frequency.
The zero sequence voltage component can be processed by the algorithm in the same way.
And combining an improved VMD center frequency self-adaptive selection principle, and decomposing the zero sequence current and the zero sequence voltage to obtain corresponding transient values.
And 5, performing Hilbert transformation on the transient state quantity of each line, and selecting lines by combining a phase comparison line selection method.
The Hilbert transform can be seen as passing the original signal through a filter or a system. The transient is Hilbert transformed to generate a complex signal comprising the phase information of the original signal.
The extraction of phase information from the results of the Hilbert transform can be achieved by calculating the amplitude and phase angle of the complex signal.
The result of processing the fault component through the Hilbert transform is that a one-dimensional fault characteristic component signal is converted into a two-dimensional signal on a complex plane, and the complex modes and the amplitude angles represent the amplitude and the phase of the signal, so that the phase angle can be extracted from the result of processing the fault component through the Hilbert transform, and a specific phase angle or frequency component can be obtained from the extracted phase information.
The phase criterion of the selected line is specifically: the zero sequence current phase angle of the fault line is 90 degrees different from that of the normal line. After the phase angle information is obtained, the fault line can be determined according to the phase criterion.
Based on the same technical concept, the embodiment also provides a transient line selection system for a single-phase earth fault of a power distribution network ring network, as shown in fig. 3, and the transient line selection system specifically comprises:
the simulation model building unit is used for building a small-current grounding distribution network ring network simulation model;
and the data monitoring unit is used for recording three-phase current and three-phase voltage of each circuit in the operation process of the looped network simulation model of the low-current grounded power distribution network in real time.
And the characteristic extraction unit is used for extracting and obtaining the zero sequence current and the zero sequence voltage of each line based on the three-wire current and the three-phase voltage of each line.
And the variation modal decomposition unit adopts an improved variation modal decomposition algorithm to decompose the zero sequence current and zero sequence voltage of each line to obtain corresponding transient quantity.
And the conversion line selection unit performs Hilbert conversion on the transient state quantity of each line and performs line selection by combining a phase comparison line selection method.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
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 transient line selection method for the single-phase earth fault of the power distribution network ring network is characterized by comprising the following steps of:
establishing a ring network simulation model of the low-current grounding power distribution network;
recording three-phase current and three-phase voltage of each line in the running process of the looped network simulation model of the low-current grounded power distribution network in real time;
extracting zero sequence current and zero sequence voltage of each line based on three-line current and three-phase voltage of each line;
decomposing the zero sequence current and the zero sequence voltage of each circuit by adopting an improved variation modal decomposition algorithm to obtain corresponding transient values;
and carrying out Hilbert transformation on the transient state quantity of each line, and carrying out line selection by combining a phase comparison line selection method.
2. The transient line selection method for the single-phase earth fault of the power distribution network according to claim 1, wherein the building of the small-current earth power distribution network simulation model comprises the following steps:
establishing a low-current grounding distribution network ring network model in electromagnetic transient simulation software;
and adding an analog single-phase grounding fault into any line of the established low-current grounding distribution network ring network model.
3. A transient routing method for a power distribution network ring network single-phase earth fault according to claim 2, wherein the simulated single-phase earth fault is controlled by a logic time-controlled model capable of controlling the time for which the simulated single-phase earth fault is initiated and sustained.
4. The transient line selection method for the single-phase earth fault of the power distribution network ring network according to claim 1, wherein the extracted zero sequence current is the sum of three-phase currents multiplied by 1/3; the extracted zero sequence voltage is the sum of three-phase voltages and multiplied by 1/3;
and the zero sequence current and the zero sequence voltage are obtained through the cooperation calculation of an adder and a multiplier.
5. The transient line selection method for a single-phase earth fault of a power distribution network ring network according to any one of claims 1 to 4, wherein the improved variational modal decomposition algorithm specifically comprises:
selecting a preset scale in the variation modal decomposition algorithm based on a time-frequency entropy stabilization criterion;
and selecting punishment parameters in the variation modal decomposition algorithm based on a multi-scale sample entropy minimum criterion.
6. The transient line selection method for the single-phase earth fault of the power distribution network ring network according to claim 5, wherein the selection of the preset scale in the variation modal decomposition algorithm based on the time-frequency entropy stabilization criterion comprises the following steps:
the components obtained through decomposition of the variation modal decomposition algorithm under different preset scale values are subjected to Hilbert variation to obtain amplitude superposition of the same points of the instantaneous frequency, and a sparse matrix is constructed;
dividing the sparse matrix into equal area areas, and obtaining a time-frequency entropy value;
and determining an optimal preset scale value in the variation modal decomposition algorithm according to the time-frequency entropy value.
7. The transient state route selection method for the single-phase earth fault of the power distribution network ring network according to claim 5, wherein the transient state quantity of each route is subjected to Hilbert transformation, and the method specifically comprises the following steps:
performing Hilbert transformation on the transient state quantity of each line to generate a complex signal;
the amplitude and phase angle of the complex signal are calculated.
8. The transient line selection method for the single-phase earth fault of the power distribution network ring network according to claim 7, wherein the line selection is performed by combining a phase comparison line selection method, and the method specifically comprises the following steps:
and determining a fault line according to the phase angles of the lines and combining phase criteria of the selected lines.
9. The transient line selection method for the single-phase earth fault of the power distribution network according to claim 8, wherein the phase criterion is specifically: the zero sequence current phase angle of the fault line is 90 degrees different from that of the normal line.
10. A transient line selection system for a single-phase earth fault of a power distribution network ring network, the transient line selection system comprising:
the simulation model building unit is used for building a ring network simulation model of the low-current grounding power distribution network;
the data monitoring unit is used for recording three-phase current and three-phase voltage of each line in the running process of the looped network simulation model of the low-current grounded power distribution network in real time;
the characteristic extraction unit is used for extracting and obtaining zero sequence currents and zero sequence voltages of all the lines based on the three-phase currents and the three-phase voltages of all the lines;
the variation modal decomposition unit adopts an improved variation modal decomposition algorithm to decompose the zero sequence current and the dummy voltage of each line to obtain corresponding transient quantity;
and the transformation line selection unit is used for carrying out Hilbert transformation on the transient state quantity of each line and selecting lines by combining a phase comparison line selection method.
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