CN112578228A - Zero-sequence-independent single-phase earth fault discrimination algorithm for power distribution network - Google Patents
Zero-sequence-independent single-phase earth fault discrimination algorithm for power distribution network Download PDFInfo
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- 238000005070 sampling Methods 0.000 claims abstract description 8
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- 238000004088 simulation Methods 0.000 abstract description 11
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- G—PHYSICS
- 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
- 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
- G01R31/088—Aspects of digital computing
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- G—PHYSICS
- 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
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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Abstract
The invention relates to a zero sequence independent power distribution network single-phase earth fault discrimination algorithm, which comprises the following steps of S1: collecting three-phase voltage and current, and recording an original sampling waveform; s2: respectively carrying out Fourier operation on the three-phase voltage and the three-phase current to obtain respective steady-state fundamental wave amplitude values; s3: increasing instantaneous mutation of phase voltage, triggering a fault judgment process when the mutation proportion reaches a set threshold value kU, and entering S4; s4: checking the steady-state three-phase current before and after the phase voltage transient, and judging whether the quotient of the sum of the maximum amplitude of the maximum current change of the first phase and the amplitude of the maximum current change of the second and third phases and the value of the sum exceeds a preset value kI or not in the same time period; s5: and detecting the transient three-phase current change trend before the phase voltage is transient. According to the invention, fault discrimination is carried out according to the change characteristics of phase current when the single-phase ground fault occurs, and the single-phase ground fault with the ground resistance within 8000 omega can be accurately and effectively detected according to the simulation result, so that the accuracy of single-phase ground fault discrimination is greatly improved.
Description
Technical Field
The invention relates to a fault discrimination algorithm, in particular to a single-phase earth fault discrimination algorithm for a power distribution network.
Background
Most of power distribution networks in China are neutral point ungrounded systems, and when single-phase ground faults occur, zero-sequence current amplitude is small and discrimination difficulty is high. At present, domestic main stream manufacturers of power distribution terminal equipment adopt a zero sequence small signal parameter identification method to judge single-phase earth faults, the technology is greatly influenced by the precision of an external transformer, and only single-phase earth faults with the earth resistance below 1000 omega can be accurately judged; the method can not accurately judge the single-phase earth fault under the conditions of large resistance and ultra-large resistance earthing.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to overcome the defects in the prior art, provides a power distribution network single-phase earth fault discrimination algorithm independent of zero sequence, carries out fault discrimination according to the change characteristics of phase current when a single-phase earth fault occurs, can accurately and effectively detect the single-phase earth fault with the earth resistance within 8000 omega according to a simulation result, and greatly improves the single-phase earth fault discrimination accuracy.
The technical scheme is as follows: in order to solve the technical problem, the invention discloses a single-phase earth fault discrimination algorithm of a power distribution network independent of zero sequence, which comprises the following steps,
s1: collecting three-phase voltage and three-phase current, and recording an original sampling waveform, wherein the sampling frequency is more than or equal to 12.8 kHz;
s2: respectively carrying out Fourier operation on the three-phase voltage and the three-phase current to obtain respective steady-state fundamental wave amplitude values;
s3: increasing instantaneous mutation of phase voltage, triggering a fault judgment process when the mutation proportion reaches a set threshold value kU, and entering S4;
s4: checking the steady-state three-phase current before and after the phase voltage transient, and judging whether the quotient of the sum of the maximum amplitude of the maximum current change of the first phase and the amplitude of the maximum current change of the second and third phases and the value thereof exceeds a preset value kI or not in the same time period, wherein the formula is expressed as (assuming that the A phase is a fault phase)
If k is larger than kI, the fault is in the area, and S6 is skipped to give a single-phase grounding area fault conclusion; if k is less than or equal to kI, entering S5 for transient judgment;
s5: detecting the change trend of transient three-phase current before the phase voltage is transient, if a certain phase change trend is opposite to other two phases, judging that the single-phase grounding region has an internal fault, and jumping to S6 to give a fault conclusion in the single-phase grounding region; if the reverse situation does not occur, namely the fault outside the single-phase grounding area is judged, S6 is skipped to give a conclusion of the fault outside the single-phase grounding area;
s6: and (5) obtaining a fault conclusion.
The basic principle of the invention is as follows: and detecting the earth fault of the three-phase power distribution network by using transient state and steady state phase current information in the system, and realizing fault positioning and isolation.
When a ground fault occurs, fault current flows to a fault line through a fault point, no fault current passes through the line behind the fault point, and when the fault occurs, the grid current changes suddenly, the three-phase current value of a fault area changes greatly, while the three-phase current value of a non-fault sound area changes slightly, the waveform is approximate, and the characteristic that the three-phase current is asymmetric is presented.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:
(1) only three-phase current is needed to be measured, and zero-sequence voltage and zero-sequence current do not need to be detected;
(2) the sensitivity is high, high-resistance grounding faults can be effectively detected, and grounding resistance of up to 8000 ohms can be detected under the simulation condition;
(3) the detection is independent of the load current, and the change of the load is natural and symmetrical;
(4) the detection is irrelevant to the tuning condition of the arc suppression coil of the system, and the tuning condition of the arc suppression coil of the power grid system cannot influence the measurement result of the device;
(5) the method is irrelevant to the capacitance to ground of the system, and the length and distribution of a feeder line of the power grid system, the size of the capacitance to ground and the like do not influence the measurement.
Drawings
FIG. 1 is a diagram of the fault analysis steps of the present invention;
FIG. 2 is a graph a of normal line current variation;
FIG. 3 is a partial enlarged view of normal line current variation;
FIG. 4 is a graph a of the line current change before the fault point of the fault line;
FIG. 5 is a graph a of line current change after a fault line fault point;
FIG. 6 is a graph b of normal line current variation;
FIG. 7 is a graph b of the line current change before the fault point of the fault line;
FIG. 8 is a graph b of the line current change after a fault line fault point;
FIG. 9 is a graph c of the line current change before the fault line fault point;
FIG. 10 is a non-fault line transient current change diagram;
FIG. 11 is a graph d of the line current change before the fault line fault point;
fig. 12 is a diagram d of the line current change after a fault line fault point.
Detailed Description
The invention is further described below with reference to the figures and examples.
1) Steady state analysis
The method is characterized in that MATLAB is imported for data analysis aiming at model data of different line topologies (2 groups of MATLAB models and 3 groups of PSCAD models-PSCAD, cable lines of an ungrounded system and an arc suppression coil grounding system, overhead lines and mixed lines) and respectively simulates the conditions of single-phase grounding when the load changes (no load-1M), grounding resistance (0.001-8000 ohm), fault time (0-90 degrees) and distribution lines are within 100 KM.
●, firstly, the condition of 0.001 ohm fault angle 0 degree of the no-ground system no-load ground resistance is analyzed, and the simulation result is shown in fig. 2, 3, 4 and 5.
● further illustrate the on-load grounding resistance of the ungrounded system of 1000 ohms, the results are shown in FIGS. 6, 7, and 8.
●, the result is shown in FIG. 9, which is finally illustrated by an ungrounded system with a ground resistance of 8000 ohms.
Simulation tests under different topologies, line lengths and various fault conditions are completed in a simulation stage, and the waveforms of the three conditions are typically displayed to obtain the following fault characteristic quantity criteria through simulation analysis.
And (3) steady-state fault characteristic analysis:
checking whether the quotient of the sum of the maximum amplitude of the maximum current change of the first phase and the amplitudes of the maximum current changes of the second and third phases and the value thereof exceeds a preset value k within the same time period, and expressing as (assuming that the A phase is a fault phase)
According to the simulation result, the value of K under various simulation states can be obtained to be generally between 2 and 5 (the value is out of the range in some cases by eliminating the problem of simulation model setting, and meanwhile, the preset value can be properly adjusted according to experience in subsequent engineering application considering that the actual system is more complicated).
2) Transient analysis
The above analysis is based on steady state asymmetry, but the method can also be used to detect transient asymmetry by appropriate filter selection and measured time periods, with simulated transient waveform current differences as shown in fig. 10, 11, 12 below.
In a transient state, because the transient maintaining time is short and the difference of waveforms is large, higher requirements are placed on the sampling speed and the reliability of the amplitude criterion of a steady state. In addition, the following algorithm can be used to detect the asymmetry according to the waveform characteristics on the basis of the above steps: the device detects the change direction of three-phase current, namely the change direction of the fault phase current difference value before a fault point is opposite to that of other phases, and the change directions detected at other detection points of a line are the same, and qualitative analysis is carried out according to the criterion.
The steady-state algorithm and the transient-state algorithm can be used in a combined mode, and are respectively judged in the wave recording data and mutually combined to improve the judgment accuracy.
As shown in fig. 1, the general steps of the present invention are as follows,
s1: collecting three-phase voltage and three-phase current, and recording an original sampling waveform, wherein the sampling frequency is more than or equal to 12.8 kHz;
s2: respectively carrying out Fourier operation on the three-phase voltage and the three-phase current to obtain respective steady-state fundamental wave amplitude values;
s3: increasing instantaneous mutation of phase voltage, triggering a fault judgment process when the mutation proportion reaches a set threshold value kU, and entering S4;
s4: checking the steady-state three-phase current before and after the phase voltage transient, and judging whether the quotient of the sum of the maximum amplitude of the maximum current change of the first phase and the amplitude of the maximum current change of the second and third phases and the value thereof exceeds a preset value kI or not in the same time period, wherein the formula is expressed as (assuming that the A phase is a fault phase)
If k is larger than kI, the fault is in the area, and S6 is skipped to give a single-phase grounding area fault conclusion; if k is less than or equal to kI, entering S5 for transient judgment;
s5: detecting the change trend of transient three-phase current before the phase voltage is transient, if a certain phase change trend is opposite to other two phases, judging that the single-phase grounding region has an internal fault, and jumping to S6 to give a fault conclusion in the single-phase grounding region; if the reverse situation does not occur, namely the fault outside the single-phase grounding area is judged, S6 is skipped to give a conclusion of the fault outside the single-phase grounding area;
s6: and (5) obtaining a fault conclusion.
The invention only needs to measure three-phase current and does not need to detect zero-sequence voltage and zero-sequence current; the sensitivity is high, high-resistance grounding faults can be effectively detected, and grounding resistance of up to 8000 ohms can be detected under the simulation condition; the detection is independent of the load current, and the change of the load is natural and symmetrical; the detection is irrelevant to the tuning condition of the arc suppression coil of the system, and the tuning condition of the arc suppression coil of the power grid system cannot influence the measurement result of the device; the method is irrelevant to the capacitance to ground of the system, and the length and distribution of a feeder line of the power grid system, the size of the capacitance to ground and the like do not influence the measurement.
The present invention provides a thought and a method, and a method and a way for implementing the technical scheme are many, the above is only a preferred embodiment of the present invention, it should be noted that, for a person skilled in the art, a plurality of improvements and modifications can be made without departing from the principle of the present invention, and the improvements and modifications should be regarded as the protection scope of the present invention, and each component not explicitly described in the embodiment can be implemented by the prior art.
Claims (1)
1. A single-phase earth fault discrimination algorithm of a power distribution network independent of zero sequence is characterized in that: which comprises the following steps of,
s1: collecting three-phase voltage and three-phase current, and recording an original sampling waveform, wherein the sampling frequency is more than or equal to 12.8 kHz;
s2: respectively carrying out Fourier operation on the three-phase voltage and the three-phase current to obtain respective steady-state fundamental wave amplitude values;
s3: increasing instantaneous mutation of phase voltage, triggering a fault judgment process when the mutation proportion reaches a set threshold value kU, and entering S4;
s4: checking the steady-state three-phase current before and after the phase voltage transient, and judging whether the quotient of the sum of the maximum amplitude of the maximum current change of the first phase and the amplitude of the maximum current change of the second and third phases and the value thereof exceeds a preset value kI or not in the same time period, wherein the formula is expressed as (assuming that the A phase is a fault phase)
If k is larger than kI, the fault is in the area, and S6 is skipped to give a single-phase grounding area fault conclusion; if k is less than or equal to kI, entering S5 for transient judgment;
s5: detecting the change trend of transient three-phase current before the phase voltage is transient, if a certain phase change trend is opposite to other two phases, judging that the single-phase grounding region has an internal fault, and jumping to S6 to give a fault conclusion in the single-phase grounding region; if the reverse situation does not occur, namely the fault outside the single-phase grounding area is judged, S6 is skipped to give a conclusion of the fault outside the single-phase grounding area;
s6: and (5) obtaining a fault conclusion.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114371359A (en) * | 2022-01-21 | 2022-04-19 | 宁波箭隆电子有限公司 | Transient event detection method and power quality detection equipment |
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- 2020-12-17 CN CN202011493944.9A patent/CN112578228A/en active Pending
Patent Citations (7)
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Application publication date: 20210330 |