CN110426604B - Single-phase earth fault line selection method of resonance earthing system - Google Patents

Single-phase earth fault line selection method of resonance earthing system Download PDF

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CN110426604B
CN110426604B CN201910825474.2A CN201910825474A CN110426604B CN 110426604 B CN110426604 B CN 110426604B CN 201910825474 A CN201910825474 A CN 201910825474A CN 110426604 B CN110426604 B CN 110426604B
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amplitude
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刘鹏辉
刘永辉
杨海柱
江昭阳
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Henan University of Technology
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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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    • 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
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Abstract

The invention discloses a single-phase earth fault line selection method of a resonance grounding system, belongs to the technical field of power system relay protection, and aims to solve the technical problem of fault feeder line identification when a single-phase earth fault occurs in the resonance grounding system. The method comprises the following steps: acquiring zero sequence current at the head end of a feeder line; acquiring a fundamental wave amplitude, a second harmonic amplitude and a third harmonic amplitude, and normalizing the fundamental wave amplitude, the second harmonic amplitude and the third harmonic amplitude according to the ratio of the fundamental wave amplitude, the second harmonic amplitude and the third harmonic amplitude to the sum of all feeder line harmonic amplitudes; solving a characteristic coefficient by using a least square fitting method; and finally, identifying the fault feeder line through the characteristic coefficient. The method is not limited by the unfavorable factors of the arc suppression coil, utilizes the compensation characteristics of the arc suppression coil in different frequency domains on the fault feeder line to form fault line selection, and has the advantages of strong anti-interference performance, high line selection accuracy, easiness in engineering realization and the like.

Description

Single-phase earth fault line selection method of resonance earthing system
Technical Field
The invention relates to the technical field of power system relay protection, in particular to a single-phase earth fault line selection method for a resonance grounding system.
Background
The long-term operation experience and operation practice result in that the neutral point of the power distribution network in China widely adopts a low-current grounding operation mode, which mainly comprises two modes of ungrounded mode and resonant grounding mode. The low current grounding operation mode has obvious advantages: when a single-phase earth fault occurs in the power distribution network, the fault current is similar to the load current in value due to the extremely high impedance of a fault loop, and the protection does not need to act immediately; the three-phase line voltage of the system still keeps symmetry, and the distribution network still has the ability of providing uninterrupted power supply for the load. Therefore, the operation rule allows the low-current grounding system to operate with a fault for 1-2 hours. However, the neutral point low current grounding operation mode has natural defects: under the condition of single-phase earth faults, the fault characteristics of the power distribution network are not obvious enough, and great difficulty is brought to fault detection and fault line selection.
In order to solve the problem of fault line selection of a low-current grounding system, experts and scholars at home and abroad develop extensive and deep research and obtain certain effect. The fault line selection methods disclosed in the prior art can be classified into injection signal analysis methods, steady-state component methods, transient component methods and the like. The injection signal analysis method has strong flexibility and high reliability; however, this method requires additional auxiliary electrical devices, and the method injects a specific electrical signal into the system, which is likely to cause interference with other devices. The steady-state component method has extremely high reliability in ungrounded systems, but its reliability tends to become poor when applied to resonant grounded systems. The transient component method is less influenced by the compensation effect of the arc suppression coil, is greatly concerned in recent years and becomes a research hotspot; however, the accuracy of the method in identifying the high-resistance ground fault is low, the method is easily interfered by other transient processes in the system, and the application effect in the actual engineering is not expected.
In summary, the existing fault line selection method is not complete. The problem of faulty line selection remains particularly troublesome in resonant grounded systems. Particularly, for a ground fault with a high transition resistance, the fault line selection accuracy of the existing method in actual engineering is often low, and the increasingly improved relay protection reliability requirement cannot be met.
Under the background, the problem of single-phase earth fault line selection of the resonance grounding system is not effectively solved, and the single-phase earth fault line selection method becomes a practical problem which puzzles field operation and maintenance personnel for a long time.
Disclosure of Invention
The invention aims to provide a single-phase earth fault line selection method of a resonance earthing system aiming at the defects of the existing fault line selection technology.
The invention relates to a single-phase earth fault line selection method of a resonance grounding system, which is realized by the following technical scheme:
step 1: the method comprises the following steps that a protection device is arranged at the head end of each feeder line on the same bus in a resonant grounding system, and the protection device monitors the feeder lines in real time; after the single-phase earth fault of the resonance earth system is judged, sampling is carried out on the zero-sequence current signal flowing through the head end of each feeder line to obtain a sampling data sequence
Figure GDA0003008911780000021
Wherein k is a serial number of a feeder line, and N is the total sampling times in a power frequency period;
step 2: from the data sequence
Figure GDA0003008911780000022
Extracting fundamental component information and attenuated direct current component information of the signal, wherein M is 0.5N; the extracted radicalsThe wave component information includes a fundamental amplitude
Figure GDA0003008911780000023
And fundamental phase angle theta(k)The extracted attenuated DC component information includes an initial attenuation amplitude D(k)And decay time constant τ(k)；
And step 3: according to the formula (1), filtering fundamental wave component and attenuation direct current component from zero sequence current signal to obtain data sequence
Figure GDA0003008911780000024
Figure GDA0003008911780000025
And 4, step 4: from the data sequence
Figure GDA0003008911780000026
Second harmonic amplitude of the extracted signal
Figure GDA0003008911780000027
Amplitude of third harmonic
Figure GDA0003008911780000028
And 5: amplitude of fundamental wave according to equation (2)
Figure GDA0003008911780000029
Second harmonic amplitude
Figure GDA00030089117800000210
And third harmonic amplitude
Figure GDA00030089117800000211
Carrying out normalization processing to obtain a data sequence after normalization processing
Figure GDA00030089117800000212
Figure GDA00030089117800000213
Wherein P is the total number of feeders;
step 6: for data sequence
Figure GDA00030089117800000214
Fitting is performed to obtain a characteristic coefficient { F(1),F(2),…,F(P)}；
And 7: for characteristic coefficient { F(1),F(2),…,F(P)Screening the elements in the power line, finding out the element with the largest numerical value, assigning the serial number of the element to a variable w, and finally judging that the w-th feeder line is the feeder line where the single-phase earth fault is located.
Preferably, wherein in step 6 the characteristic coefficients { F }(1),F(2),…,F(P)Obtaining according to the formula (3):
Figure GDA0003008911780000031
in the formula (I), the compound is shown in the specification,
Figure GDA0003008911780000032
E(k)is the process coefficient.
The basic principle of the method of the invention is as follows:
the difficulty of implementing fault line selection for a resonant grounded system, as distinguished from an ungrounded system, is: when single-phase earth fault occurs, the arc suppression coil generates inductive zero-sequence current to compensate the capacitive fault current, and further weaken the fault characteristics. Therefore, the compensation function of the arc suppression coil increases the difficulty of fault line selection. However, from another perspective, the compensation of the crowbar coil is mainly reflected on the fault line and is more frequency sensitive. Therefore, the method of the invention is not limited by the unfavorable factors of the arc suppression coil, and the compensation characteristics of the arc suppression coil on the fault feeder line in different frequency domains are utilized to form the fault line selection.
The compensation characteristics of the arc suppression coil in different frequency domains are as follows:
the relation between the arc suppression coil and the compensated capacitance is shown as the following formula (4):
Figure GDA0003008911780000033
in the formula, L is the inductance value of the arc suppression coil, C is the capacitance value compensated by the arc suppression coil, the compensation function of the arc suppression coil can be represented, and omega is the angular frequency.
Substituting omega-2 pi f into formula (4) to obtain the product
Figure GDA0003008911780000034
Wherein f is the frequency.
As can be seen from equation (5), the compensation effect of the arc suppression coil is inversely proportional to the square of the frequency. As can be seen from the analysis of the fundamental wave (f is 50Hz), the second harmonic (f is 100Hz), and the third harmonic (f is 150Hz), the compensation of the second harmonic by the arc suppression coil is one fourth of the compensation of the fundamental wave, and the compensation of the third harmonic is one ninth of the compensation of the fundamental wave, as shown in fig. 1 of the drawings.
For a resonant grounding system, the zero sequence current measured by the healthy feeder line head end protection device is the capacitance current of the feeder line; the zero sequence current measured by the fault feeder line head end protection device is the sum of the arc suppression coil compensation current and all healthy feeder line capacitance currents. The above-mentioned compensation of the crowbar coil is therefore mainly present in the fault line. The fault line selection can be realized through the compensation characteristic of the arc suppression coil.
The compensation characteristic described above is reflected in relative values. The absolute value of the amplitude of each harmonic is measured by the protection device, not the relative value. Thus, the method of the present invention is directed to the fundamental amplitude according to equation (2)
Figure GDA0003008911780000035
Second harmonic amplitude
Figure GDA0003008911780000036
And third harmonic amplitude
Figure GDA0003008911780000041
Carrying out normalization processing to obtain a normalized data sequence
Figure GDA0003008911780000042
Wherein the content of the first and second substances,
Figure GDA0003008911780000043
represents
Figure GDA0003008911780000044
The sum of all feeder line fundamental wave amplitude values
Figure GDA0003008911780000045
The ratio of (A) to (B);
Figure GDA0003008911780000046
represents
Figure GDA0003008911780000047
The sum of the amplitudes of the second harmonic of all the feeder lines
Figure GDA0003008911780000048
The ratio of (A) to (B);
Figure GDA0003008911780000049
represents
Figure GDA00030089117800000410
The sum of the third harmonic amplitudes of all the feeder lines
Figure GDA00030089117800000411
The ratio of (a) to (b).
Based on the compensation characteristics of the arc suppression coil, the data sequence can be obtained after analysis
Figure GDA00030089117800000412
Variations of (2)The trend will be approximately obeyed
Figure GDA00030089117800000413
The method uses a least square method to fit the characteristic coefficients, and characteristic coefficients { F ] are obtained according to a formula (3)(1),F(2),…,F(P)}. For a robust feeder line, the feeder line is,
Figure GDA00030089117800000414
showing a decreasing trend of change, the obtained F(k)The value of (a) is small and generally negative; in the case of a faulty feeder line,
Figure GDA00030089117800000415
showing an increasing trend of change, the obtained F(k)The value of (a) is positive and significantly greater than a sound feeder.
Based on the analysis, the method of the invention discriminates through { F }(1),F(2),…,F(P)Finding out the element with the maximum value from the values of the single-phase grounding fault, and determining the feeder where the single-phase grounding fault is located.
Herein, the pair
Figure GDA00030089117800000416
{F(1),F(2),…,F(P)The following brief description is made:
amplitude of fundamental wave
Figure GDA00030089117800000417
From the data sequence
Figure GDA00030089117800000418
Extracting. According to the formula (1), filtering fundamental wave component and attenuation direct current component from zero sequence current signal to obtain data sequence
Figure GDA00030089117800000419
Then, from the data sequence
Figure GDA00030089117800000420
Extract two of the signalSubharmonic amplitude
Figure GDA00030089117800000421
Amplitude of third harmonic
Figure GDA00030089117800000422
Coefficient of characteristics F(1),F(2),…,F(P)The value of the equation is obtained by a least square fitting method, and a specific calculation formula is shown in the formula (3).
The implementation steps of the fault line selection method of the invention are shown in figure 2 of the accompanying drawings.
The invention has the following advantages and effects: 1) the basic principle of the method is established on the basis of single-phase earth fault mechanism analysis, and the implementation method is practically adaptive to the actual fault processing of the power distribution network, so that the engineering implementation is facilitated. 2) The method has high fault line selection accuracy and is still reliable and effective under the condition of higher fault resistance. 3) The method of the invention can solve the characteristic coefficient by a least square fitting method, and has stronger anti-interference performance.
Drawings
Fig. 1 is a schematic diagram of compensation effects of arc suppression coils in different frequency domains.
Fig. 2 is a flow chart of the method for implementing fault line selection according to the present invention.
FIG. 3 is a diagram of a simulation model according to an embodiment of the present invention.
Fig. 4 is a waveform diagram of zero sequence current of the feeder line in the embodiment of the present invention.
Detailed Description
The present invention is described in further detail with reference to the following examples. It should be noted that the following example is only one practical implementation of the present invention, and is only used to more clearly illustrate the specific implementation of the method of the present invention, but the implementation of the present invention is not limited to this example.
Example (b):
fig. 3 is a diagram of a simulation model of single-phase grounding of the resonant grounding system of this embodiment. The system is a 10kV power distribution network system, and the system frequency is 50 Hz. The bus is connected with 4 feeder lines (feeder line 1-feeder line 4), and the length of the feeder lines is 6km, 7km, 4km and 7km in sequence. The arc suppression coil compensates the system capacitance through the grounding transformer. When t is 0.112s, a B-phase grounding fault occurs on the feeder 2 at a distance of 3.5km from the head end of the feeder.
According to the single-phase earth fault line selection method of the resonant grounding system, the fault line selection is implemented through the following steps:
step 1: the method comprises the following steps that a protection device is arranged at the head end of each feeder line on the same bus in the resonant grounding system, and the protection device monitors the feeder lines in real time; after the single-phase earth fault of the system is judged, sampling is carried out on the zero-sequence current signal flowing through the head end of each feeder line at the sampling frequency of 6000Hz to obtain a sampling data sequence of 1.5 power frequency periods after the fault
Figure GDA0003008911780000051
Wherein k is a serial number of a feeder line, and N is 120 which is the total sampling times in a power frequency period; the waveform of the collected current is shown in fig. 4;
step 2: from the data sequence
Figure GDA0003008911780000052
Extracting fundamental component information and attenuated direct current component information of the signal, wherein M is 0.5N 60; the extracted fundamental component information includes a fundamental amplitude
Figure GDA0003008911780000053
And fundamental phase angle theta(k)The extracted attenuated DC component information includes an initial attenuation amplitude D(k)And decay time constant τ(k)；
Specifically, the fundamental amplitude in this embodiment is
Figure GDA0003008911780000054
The fundamental phase angle (expressed in radians here) is θ(1)＝2.214，θ(2)＝2.154，θ(3)＝2.214，θ(4)＝2.212，
Initial attenuation amplitude of D(1)＝0.005，D(2)＝-3.171，D(3)＝0.004，D(4)＝0.009，
Decay time constant of τ(1)＝0.017，τ(2)＝0.032，τ(3)＝0.006，τ(4)＝0.013；
And step 3: according to the formula (1), filtering fundamental wave component and attenuation direct current component from zero sequence current signal to obtain data sequence
Figure GDA0003008911780000055
And 4, step 4: from the data sequence
Figure GDA0003008911780000056
Second harmonic amplitude of the extracted signal
Figure GDA0003008911780000057
Amplitude of third harmonic
Figure GDA0003008911780000058
Specifically, in the present embodiment, the second harmonic amplitude is
Figure GDA0003008911780000059
Figure GDA00030089117800000510
Third harmonic amplitude of
Figure GDA00030089117800000511
And 5: amplitude of fundamental wave according to equation (2)
Figure GDA0003008911780000061
Second harmonic amplitude
Figure GDA0003008911780000062
And third harmonic amplitude
Figure GDA0003008911780000063
Carrying out normalization processing to obtain a normalized data sequence
Figure GDA0003008911780000064
Specifically, in the present embodiment,
Figure GDA0003008911780000065
Figure GDA0003008911780000066
Figure GDA0003008911780000067
Figure GDA0003008911780000068
step 6: for data sequence
Figure GDA0003008911780000069
Fitting is performed, and a characteristic coefficient { F is obtained by a least square fitting formula shown in formula (3)(1),F(2),F(3),F(4)}＝{-0.023,0.182,-0.070,-0.088}；
And 7: for characteristic coefficient { F(1),F(2),F(3),F(4)Screening the elements in the data, and finding out the element with the largest numerical value as F(2)Then, the 2 nd feeder (i.e. feeder 2) is finally determined to be the feeder where the single-phase ground fault is located.
In the embodiment, the fault line selection result is consistent with the preset fault condition. The method can accurately find out the fault feeder line, and the effectiveness of the method is verified.
The above-mentioned embodiments are only preferred embodiments of the present invention, not all of them, but the protection scope of the present invention is not limited to the above-mentioned embodiments, and the specific protection scope is subject to the claims. It should be understood that various changes, substitutions and alterations in form and detail could be made herein without departing from the spirit and principles of the invention.

Claims (2)

1. A single-phase earth fault line selection method of a resonance grounding system is characterized by comprising the following steps:
step 1: the method comprises the following steps that a protection device is arranged at the head end of each feeder line on the same bus in a resonant grounding system, and the protection device monitors the feeder lines in real time; after the single-phase earth fault of the resonance earth system is judged, sampling is carried out on the zero-sequence current signal flowing through the head end of each feeder line to obtain a sampling data sequence
Figure FDA0003008911770000011
Wherein k is a serial number of a feeder line, and N is the total sampling times in a power frequency period;
step 2: from the data sequence
Figure FDA0003008911770000012
Extracting fundamental component information and attenuated direct current component information of the signal, wherein M is 0.5N; the extracted fundamental component information includes a fundamental amplitude
Figure FDA0003008911770000013
And fundamental phase angle theta(k)The extracted attenuated DC component information includes an initial attenuation amplitude D(k)And decay time constant τ(k)；
And step 3: according to the formula (1), filtering fundamental wave component and attenuation direct current component from zero sequence current signal to obtain data sequence
Figure FDA0003008911770000014
Figure FDA0003008911770000015
And 4, step 4: from the data sequence
Figure FDA0003008911770000016
Second harmonic amplitude of the extracted signal
Figure FDA0003008911770000017
Amplitude of third harmonic
Figure FDA0003008911770000018
And 5: amplitude of fundamental wave according to equation (2)
Figure FDA0003008911770000019
Second harmonic amplitude
Figure FDA00030089117700000110
And third harmonic amplitude
Figure FDA00030089117700000111
Carrying out normalization processing to obtain a data sequence after normalization processing
Figure FDA00030089117700000112
Figure FDA00030089117700000113
Wherein P is the total number of feeders;
step 6: for data sequence
Figure FDA00030089117700000114
Fitting is performed to obtain a characteristic coefficient { F(1),F(2),…,F(P)}；
And 7: for characteristic coefficient { F(1),F(2),…,F(P)Screening the elements in the test strip, and screening the elements,and finding out the element with the maximum numerical value, assigning the serial number of the element to a variable w, and finally judging that the w-th feeder is the feeder where the single-phase earth fault is located.
2. The single-phase earth fault line selection method of the resonant grounding system as claimed in claim 1, wherein the characteristic coefficient { F in the step 6(1),F(2),…,F(P)Obtaining according to the formula (3):
Figure FDA0003008911770000021
in the formula (I), the compound is shown in the specification,
Figure FDA0003008911770000022
E(k)is the process coefficient.
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