CN110441641B - Low-current grounding line selection method and system based on zero-sequence direct-current component - Google Patents
Low-current grounding line selection method and system based on zero-sequence direct-current component Download PDFInfo
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- CN110441641B CN110441641B CN201910670791.1A CN201910670791A CN110441641B CN 110441641 B CN110441641 B CN 110441641B CN 201910670791 A CN201910670791 A CN 201910670791A CN 110441641 B CN110441641 B CN 110441641B
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
Abstract
The invention discloses a small current grounding line selection method and a small current grounding line selection system based on zero sequence direct current components, wherein the method comprises the steps of sampling zero sequence voltage and zero sequence current of each line in a power grid, judging whether zero sequence voltage mutation occurs according to the zero sequence voltage obtained by sampling, and further judging whether the zero sequence voltage mutation is caused by single-phase grounding faults; and finally, judging the line with the single-phase earth fault based on the variable quantity of the direct-current components of the zero-sequence current before and after the single-phase earth fault occurs. Aiming at the running mode that the neutral point is grounded through the arc suppression coil, the invention can reliably avoid the condition of inaccurate line selection result caused by zero crossing points or grounding through high resistance, improve the accuracy of low-current grounding line selection and improve the running reliability of the power system.
Description
Technical Field
The invention relates to the technical field of power system automation, in particular to a small current grounding line selection method and system based on zero sequence direct current components.
Background
The 6-66 kV power distribution network in China mostly adopts a low-current grounding operation mode. After a single-phase earth fault occurs in a low-current earth grid, a large short-circuit current cannot be generated, but the short-circuit current is not a little harmful, and in order to establish a safe and good power environment, an earth line should be found as soon as possible and cut off. Most of the traditional line selection methods are based on fault steady-state signals, namely a zero-sequence reactive power direction method, but for a system with a neutral point grounded through an arc suppression coil, the line selection method is invalid because power frequency steady-state quantity is compensated by inductive current. Therefore, for a neutral point arc suppression coil grounding system, the harmonic component in the zero sequence current and the zero sequence voltage transient signal is extracted mostly, and the line selection is carried out by analyzing the relationship between the harmonic component and the zero sequence voltage transient signal. However, when a ground fault occurs at a zero-crossing point or via a high resistance, the transient amount is greatly suppressed, and the method of discriminating using a harmonic component becomes insensitive. Under the above conditions, the zero sequence current only has a steady-state component to a great extent, and under the condition that the criterion of the steady-state component cannot be used, the fault line can hardly be found by using a discrimination method related to the transient-state component.
Disclosure of Invention
The invention aims to provide a small current grounding line selection method based on a zero sequence direct current component aiming at the operation mode that a neutral point is grounded through an arc suppression coil, which can reliably avoid the condition of inaccurate line selection result caused by zero crossing points or grounding through high resistance, improve the accuracy of small current grounding line selection and improve the reliability of the operation of a power system.
The technical scheme adopted by the invention is as follows: a small current grounding line selection method based on zero sequence direct current components comprises the following steps:
sampling zero sequence voltage and zero sequence current of each line in a small current grounding power grid;
judging whether each line has zero-sequence voltage mutation or not according to the zero-sequence voltage obtained by sampling;
responding to the zero sequence voltage mutation of any line, and judging whether the zero sequence voltage mutation is caused by the single-phase earth fault of the system;
and judging the line with the single-phase earth fault according to the variable quantity of the direct-current component of the zero-sequence current of each line before and after the zero-sequence voltage mutation moment on the basis of the symmetry of the three-phase line voltage of the system in response to the zero-sequence voltage mutation caused by the single-phase earth fault of the system.
The invention relates to a method for selecting lines by utilizing transient direct current components in zero sequence current, which aims at the condition that the traditional zero sequence reactive power cannot be utilized to perform fault line selection due to the operation mode of inductive current overcompensation when a system with a neutral point grounded through an arc suppression coil has a single-phase ground fault, enriches the judgment method of the grounding line selection of a power distribution network and improves the accuracy of the grounding line selection.
Preferably, the sampling frequency for sampling the zero sequence voltage and the zero sequence current of each line in the small-current grounding power grid is at least 6 kHz. Namely, the invention adopts high-frequency sampling, and can improve the reliability of fault identification.
Preferably, the basis for judging the zero sequence voltage mutation of the line is as follows: the variation of a zero-sequence voltage sampling value between a current sampling point k and a sampling point (k-N) before a cycle is larger than a preset mutation threshold value; and N is the number of sampling points of each cycle under the current sampling frequency. In order to make the start of the line selection less sensitive, the threshold for the amount of the jump may be a slightly larger value, and may be an empirical value.
In a low-current grounding power grid, each line is connected to the same bus, so that the voltage sudden change time of each line, namely the fault time, should be the same theoretically.
Preferably, the method for judging the occurrence of the single-phase earth fault of the system comprises the following steps:
and calculating the fundamental wave effective value of the zero-sequence voltage of each sampling point in the cycle after the zero-sequence voltage mutation moment of the line, and if the fundamental wave effective value of the zero-sequence voltage of any sampling point of any line is greater than a preset zero-sequence voltage starting threshold value, the system has single-phase earth fault. Otherwise, the sudden change of the zero sequence voltage is caused by the interference in the system, and the grounding line selection judgment is not needed to be carried out any more. When single-phase earth fault occurs, the three line voltages of each line in the system are still symmetrical, and at the moment, when the sudden change of the zero sequence voltage is caused by the single-phase earth fault, the judgment of earth selection can be continuously carried out. The zero sequence voltage starting threshold value can be an empirical value.
Preferably, the determining the line with the single-phase ground fault based on the variation of the zero-sequence current direct-current component of each line before and after the zero-sequence voltage abrupt change time includes, for each line with the zero-sequence voltage abrupt change:
acquiring zero-sequence current sampling point data of each cycle before and after the zero-sequence voltage mutation moment;
calculating the variable quantity of the direct current component of the zero-sequence current before and after the zero-sequence voltage mutation moment;
and comparing the calculated variation of the zero-sequence direct-current component with a preset zero-sequence direct-current component line selection judgment threshold value, and if the variation of the zero-sequence direct-current component reaches or exceeds the preset zero-sequence direct-current component line selection judgment threshold value, judging that a corresponding line has a single-phase earth fault.
Preferably, the zero sequence direct current components before and after the fault occurrence time are obtained by adopting a fourier algorithm, or the average value of the zero sequence current sampling point values of the corresponding cycle is taken. Other existing algorithms may also be used depending on the actual situation.
Preferably, the zero sequence direct current component line selection judgment threshold value is 101mA grade. That is, the invention uses the variable quantity of the direct current component obtained by the first cycle calculation after the fault to judge the direct current component mutation threshold value of the single-phase earth fault line, which is generally set to be dozens of milliamperes, and can judge the fault with obvious direct current component.
The invention also discloses a zero sequence direct current component-based small current grounding line selection system, which comprises the following components:
the zero sequence voltage current sampling unit is used for sampling zero sequence voltage and zero sequence current of each line in the power grid;
the zero sequence voltage mutation judging unit is used for judging whether the zero sequence voltage mutation occurs to the corresponding line according to the zero sequence voltage obtained by sampling;
the system single-phase earth fault judging unit is used for judging whether the zero sequence voltage mutation of the line is caused by the single-phase earth fault when the zero sequence voltage mutation of the line occurs;
and the single-phase earth fault line distinguishing unit is used for distinguishing the line with the single-phase earth fault based on the variable quantity of the direct-current component of the zero-sequence current before and after the zero-sequence voltage mutation moment.
Advantageous effects
The method comprises the steps of sampling zero sequence voltage and zero sequence current of each line in the power system at high frequency, continuously calculating break variable of the zero sequence voltage, starting judgment of grounding line selection when the break variable of the zero sequence voltage occurs, further determining occurrence time of a fault, determining a judgment threshold value according to system electrical parameters, calculating variable quantity of direct current component of the zero sequence current after the fault occurs based on sampling point data of each cycle before and after the fault time of the zero sequence current, and finally selecting the fault line according to the comparison result of the variable quantity of the direct current component and the judgment threshold value. The method is suitable for the operation mode that the neutral point is grounded through the arc suppression coil, can reliably solve the defect that a system grounded through the arc suppression coil cannot use a steady state quantity criterion, and can conveniently and accurately analyze the fault characteristics of the zero sequence current by using a transient state quantity criterion, so that the accuracy of grounding line selection judgment is improved, the method for grounding line selection of a power distribution network is enriched, and the operation reliability of a power system is improved.
Drawings
FIG. 1 is a schematic flow chart of an embodiment of the method of the present invention.
Detailed Description
The following further description is made in conjunction with the accompanying drawings and the specific embodiments.
Example 1
The embodiment is a zero sequence direct current component-based small current grounding line selection method, which comprises the following steps:
sampling zero sequence voltage and zero sequence current of each line in a small current grounding power grid;
judging whether each line has zero-sequence voltage mutation or not according to the zero-sequence voltage obtained by sampling;
responding to the zero sequence voltage mutation of any line, and judging whether the zero sequence voltage mutation is caused by the single-phase earth fault of the system;
and judging the line with the single-phase earth fault according to the variable quantity of the direct-current component of the zero-sequence current of each line before and after the zero-sequence voltage mutation moment on the basis of the symmetry of the three-phase line voltage of the system in response to the zero-sequence voltage mutation caused by the single-phase earth fault of the system.
The invention relates to a method for selecting lines by utilizing transient direct current components in zero sequence current, which aims at the condition that the traditional zero sequence reactive power cannot be utilized to perform fault line selection due to the operation mode of inductive current overcompensation when a system with a neutral point grounded through an arc suppression coil has a single-phase ground fault, enriches the judgment method of the grounding line selection of a power distribution network and improves the accuracy of the grounding line selection.
The sampling frequency for sampling the zero sequence voltage and the zero sequence current of each line in the power grid is at least 6kHz, namely high-frequency sampling is adopted, so that the reliability of fault identification can be improved.
During sampling, the zero sequence voltage mutation quantity of each line is continuously calculated, so that the judgment of grounding line selection is started when the zero sequence voltage mutation occurs to the line. The judgment basis of the sudden change of the zero sequence voltage of the line is as follows: the variation of a zero-sequence voltage sampling value between a current sampling point k and a sampling point (k-N) before a cycle is larger than a preset mutation threshold value; and N is the number of sampling points of each cycle under the current sampling frequency. That is, the variation of each latest sampling point and the sampling point data before one cycle is:
u0.TBL＝u0(k)-u0(k-N) (1)
wherein u is0.TBLFor the variation of the sampled value of zero-sequence voltage, u0(k) The number of sample points is counted as k. When u is0.TBLAnd when the current is larger than the set mutation threshold value, starting judgment of grounding line selection. In order to make the start of the line selection less sensitive, the threshold for the amount of the jump may be a slightly larger value, and may be an empirical value.
If any line in the system has zero sequence voltage mutation, further judging whether the zero sequence voltage mutation of the corresponding line is caused by the single-phase earth fault of the system, namely judging whether the system has the single-phase earth fault. The method for judging the single-phase earth fault of the system comprises the following steps:
and calculating the fundamental wave effective value of the zero-sequence voltage of each sampling point in the cycle after the zero-sequence voltage mutation moment of the line, and if the fundamental wave effective value of the zero-sequence voltage of any sampling point of any line is greater than a preset zero-sequence voltage starting threshold value, the system has single-phase earth fault. Otherwise, the interference in the system is caused when the zero sequence voltage is suddenly changed, and the grounding line selection judgment is not needed to be carried out any more. When single-phase earth fault occurs, the three line voltages of each line in the system are still symmetrical, so that when the zero-sequence voltage mutation is caused by the single-phase earth fault, the judgment of earth selection can be continuously carried out. The zero sequence voltage starting threshold value can be an empirical value.
In a low-current grounding power grid, each line is connected to the same bus, so that the voltage sudden change time of each line, namely the fault time, should be the same theoretically. The invention carries out the discrimination line selection analysis of each line based on the same single-phase earth fault moment when carrying out the line selection.
A zero-sequence direct-current component line selection judgment threshold value is preset before line selection, and the threshold value is determined according to electrical parameters of the power system. Firstly, when a system with a neutral point grounded through an arc suppression coil is analyzed to generate a single-phase grounding fault, the related parameters for determining the direct current component in the zero sequence current are as follows:
suppose that after a single-phase ground fault occurs, UφIs a fault phase voltage; c is the three-phase earth capacitance of the power grid; l is0The equivalent inductance in the zero sequence loop; r is an equivalent resistor in the zero-sequence loop; l, RLThe tuning inductance and the equivalent loss resistance of the arc suppression coil, respectively, can be given by the following relations:
wherein iC0And iL0Respectively a capacitance current and an inductance current in the zero sequence current; omega is the angular frequency of the system;
the phase of the faulted phase voltage at the moment of the fault. The expression of the zero-sequence current after the single-phase earth fault occurs can be obtained from the expressions (2) and (3) as follows:
from the above formula, it can be seen that the dc component in the zero sequence current is
Wherein
Is the steady state component amplitude of the inductor current;
the phase of the fault phase voltage at the moment of fault occurrence; tau isLIs the decay time constant of the DC component of the inductance loop of the arc suppression coil.
Therefore, the dc component of the zero sequence current is mainly related to the voltage amplitude of the fault phase, the inductance and the fault phase angle, and decays exponentially, wherein the most important influencing factor is the fault phase angle
The initial value of the attenuated dc component is maximum; when in use
The starting value of the attenuated dc component is minimal. Through analyzing a plurality of simulation experiments and actual field recording waveforms, the threshold of the ground fault is judged to be 10 by utilizing the variable quantity of the direct current component obtained by calculating the first cycle after the fault1The mA level, which may be typically set to tens of milliamps. When a fault occurs, the closer the fault angle is to 0 degree, the larger the fault phase voltage is, the larger the generated direct current component is, and at the moment, the threshold value is generally dozens of milliamperes, so that the fault with obvious direct current component can be judged.
The method for judging the line with the single-phase earth fault based on the variable quantity of the direct-current components of the zero-sequence current of each line before and after the zero-sequence voltage mutation moment comprises the following steps of:
acquiring zero-sequence current sampling point data of each cycle before and after the zero-sequence voltage mutation moment;
calculating the variable quantity of the direct current component of the zero-sequence current before and after the zero-sequence voltage mutation moment;
and comparing the calculated variation of the zero-sequence direct-current component with a preset zero-sequence direct-current component line selection judgment threshold value, and if the variation of the zero-sequence direct-current component reaches or exceeds the preset zero-sequence direct-current component line selection judgment threshold value, judging that a corresponding line has a single-phase earth fault.
The zero sequence direct current component of the first cycle before and after the fault occurrence time is obtained by adopting a Fourier algorithm, or the average value or the approximate average value of the zero sequence current sampling point values of the corresponding first cycle is taken. Other existing algorithms may also be used depending on the actual situation.
Example 2
The embodiment is a zero sequence direct current component-based small current grounding line selection system, which includes:
the zero sequence voltage current sampling unit is used for sampling zero sequence voltage and zero sequence current of each line in the power grid;
the zero sequence voltage mutation judging unit is used for judging whether the zero sequence voltage mutation occurs to the corresponding line according to the zero sequence voltage obtained by sampling;
the system single-phase earth fault judging unit is used for judging whether the zero sequence voltage mutation of the line is caused by the single-phase earth fault when the zero sequence voltage mutation of the line occurs;
and the single-phase earth fault line distinguishing unit is used for distinguishing the line with the single-phase earth fault based on the variable quantity of the direct-current component of the zero-sequence current before and after the zero-sequence voltage mutation moment.
As will be appreciated by one skilled in the art, 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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. A small current grounding line selection method based on zero sequence direct current components is characterized by comprising the following steps:
sampling zero sequence voltage and zero sequence current of each line in a small current grounding power grid;
judging whether each line has zero-sequence voltage mutation or not according to the zero-sequence voltage obtained by sampling;
responding to the zero sequence voltage mutation of any line, and judging whether the zero sequence voltage mutation is caused by the single-phase earth fault of the system;
responding to the sudden change of the zero sequence voltage caused by the single-phase earth fault of the system, on the basis of the symmetry of the three-phase line voltage of the system, judging the line with the single-phase earth fault according to the variable quantity of the direct-current component of the zero sequence current of each line before and after the sudden change moment of the zero sequence voltage, wherein the judgment comprises the following steps of:
acquiring zero-sequence current sampling point data of each cycle before and after the zero-sequence voltage mutation moment;
calculating the variable quantity of the direct current component of the zero-sequence current before and after the zero-sequence voltage mutation moment;
and comparing the calculated variation of the zero-sequence direct-current component with a preset zero-sequence direct-current component line selection judgment threshold value, and if the variation of the zero-sequence direct-current component reaches or exceeds the preset zero-sequence direct-current component line selection judgment threshold value, judging that a corresponding line has a single-phase earth fault.
2. The method of claim 1, wherein the sampling frequency for sampling zero sequence voltage and zero sequence current of each line in the low current grounded power grid is at least 6 kHz.
3. The method as claimed in claim 1, wherein the zero sequence voltage sudden change of the line is determined according to the following steps: current sampling pointkAnd a sampling point of a cycle front (k-N) The variation of the zero sequence voltage sampling value is larger than a preset mutation threshold value;Nthe number of sampling points of each cycle at the current sampling frequency is adopted.
4. The method as claimed in claim 1, wherein the method for judging the single-phase earth fault of the system comprises the following steps:
and calculating the fundamental wave effective value of the zero-sequence voltage of each sampling point in the cycle after the zero-sequence voltage mutation moment of the line, and if the fundamental wave effective value of the zero-sequence voltage of any sampling point of any line is greater than a preset zero-sequence voltage starting threshold value, the system has single-phase earth fault.
5. The method as claimed in claim 1, wherein the zero sequence direct current component before and after the fault occurrence time is obtained by using a fourier algorithm, or an average value of the zero sequence current sampling point values of the corresponding one-cycle wave is taken.
6. The method as claimed in claim 1, wherein the zero sequence direct current component line selection discrimination threshold value is 101mA grade.
7. A small current grounding line selection system based on zero sequence direct current components is characterized by comprising:
the zero sequence voltage current sampling unit is used for sampling zero sequence voltage and zero sequence current of each line in the small current grounding power grid;
the zero sequence voltage mutation judging unit is used for judging whether the zero sequence voltage mutation occurs to the corresponding line according to the zero sequence voltage obtained by sampling;
the system single-phase earth fault judging unit is used for responding to zero sequence voltage mutation of any line and judging whether the zero sequence voltage mutation is caused by the system single-phase earth fault;
and a single-phase earth fault line discrimination unit, which is used for responding to the zero-sequence voltage mutation caused by the single-phase earth fault of the system, and discriminating the line with the single-phase earth fault according to the zero-sequence current direct-current component variation before and after the zero-sequence voltage mutation moment of each line on the basis of the three-phase line voltage symmetry of the system;
the method for judging the line with the single-phase earth fault comprises the following steps of:
acquiring zero-sequence current sampling point data of each cycle before and after the zero-sequence voltage mutation moment;
calculating the variable quantity of the direct current component of the zero-sequence current before and after the zero-sequence voltage mutation moment;
and comparing the calculated variation of the zero-sequence direct-current component with a preset zero-sequence direct-current component line selection judgment threshold value, and if the variation of the zero-sequence direct-current component reaches or exceeds the preset zero-sequence direct-current component line selection judgment threshold value, judging that a corresponding line has a single-phase earth fault.
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