CN113358972A - High-resistance ground fault line selection method based on line transient characteristics - Google Patents

High-resistance ground fault line selection method based on line transient characteristics Download PDF

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CN113358972A
CN113358972A CN202110607053.XA CN202110607053A CN113358972A CN 113358972 A CN113358972 A CN 113358972A CN 202110607053 A CN202110607053 A CN 202110607053A CN 113358972 A CN113358972 A CN 113358972A
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line
zero
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高锋阳
曾林
李昭君
袁成
王文祥
李明明
张浩然
罗引航
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Gansu Jiaoda Engineering Testing S&t Co ltd
Lanzhou Jiaotong University
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Lanzhou Jiaotong University
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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
    • 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
    • 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 provides a high-resistance ground fault line selection method based on line transient characteristics, which comprises the following steps: step 1, fault detection: detecting neutral point voltage to construct zero sequence voltage change gradient, and setting corresponding starting threshold value by combining 15% of traditional phase voltage as the starting of fault; step 2, analyzing the zero sequence impedance characteristic of each feeder line by using a fault equivalent circuit suitable for high-resistance grounding; step 3, analyzing to obtain that the healthy feeder line is capacitive in high and low frequency bands after the fault occurs, while the fault feeder line is capacitive in the high frequency band and inductive in the low frequency band; and 4, extracting low-frequency and high-frequency components of the transient signal by using a low-pass filter and a band-pass filter, and selecting a fault line by using the difference of the zero-sequence current of the high-low frequency section feeder line and the zero-sequence voltage correlation coefficient of the bus. The invention can solve the problem of high difficulty in detecting the high-resistance grounding fault of the power distribution network, and can accurately select the fault line under the complex environments of strong noise and the like.

Description

High-resistance ground fault line selection method based on line transient characteristics
Technical Field
The invention relates to the field of relay protection of power systems, in particular to a high-resistance ground fault line selection method based on line transient characteristics.
Background
When a high-resistance grounding fault occurs in a power distribution network resonance grounding system, the strength of a fault signal is weak, the zero sequence voltage is possibly less than 15% of a phase voltage, the zero sequence current is possibly less than 1A, a fault point is unstable, the fault detection difficulty is high, if a fault line is not selected in time to remove the fault, the long-term operation may cause large-area power failure of the power distribution network.
When the high-resistance ground faults such as conductor falling, tree flash faults and the like occur in the power distribution network, the traditional line selection method may fail under the high-resistance ground faults, and the situation that the protection device rejects action may exist in the method for detecting the faults according to the traditional operation regulations.
Most of the existing fault line selection methods use transient state quantity after fault to select lines, and the transient state quantity has the advantages of rich fault information and small influence by a neutral point connection mode. The commonly used fault line selection method based on the transient quantity mainly comprises an S transformation method, a hierarchical clustering method, a wavelet polarity method, a transient energy method and the like, and has a certain reference value for the traditional fault line selection. The S transformation method processes transient state quantity after fault, and selects fault lines by using the difference of amplitude and polarity of transient state signals such as zero sequence current and the like; the transient signals are processed by a hierarchical clustering method, but a large amount of data needs to be acquired, so that the processing difficulty is high, and the transient signals are difficult to apply to engineering; and fault line selection is carried out by a transient energy method for defining a zero sequence energy function, but the method is greatly influenced by fault transition resistance, and a fault line is difficult to detect when high-resistance grounding occurs.
Due to the fact that the grounding resistance is large when high-resistance grounding faults occur, the strength of fault signals is weak, detection difficulty is increased, fault line selection is conducted by means of single characteristic quantity, the fault line selection is difficult to adapt to the high-resistance grounding faults, misjudgment is prone to occur, the line selection device does not work, and the requirement for intelligent protection of a power distribution network is difficult to meet.
Disclosure of Invention
The invention aims to solve the defects in the prior art, provides a high-resistance grounding fault line selection method based on line transient characteristics, and solves the problem of low line selection reliability when a power distribution network is subjected to high-resistance grounding.
The invention adopts the following technical scheme:
a high-resistance grounding fault line selection method based on line transient characteristics comprises the following steps:
step 1, using a method of combining 15% of traditional phase voltage with zero sequence voltage gradient sum as a starting criterion of fault occurrence;
step 2, obtaining zero sequence current i of the circuit of two power frequency periods of the system0k(n) and bus zero sequence voltage u0(n)；
Step 3, extracting low-frequency components u of voltage and current by using low-pass and band-pass filters0l(n) and i0l(n) and a high frequency component u0h(n) and i0h(n)；
Step 4, carrying out correlation analysis on the high-low frequency component data of the voltage and the current after the fault to obtain correlation coefficients rho of corresponding high and low frequency bandsh、ρlAnd then, solving the reciprocal correlation coefficient of the line by using the correlation coefficients of the high and low frequency bands to carry out fault line selection.
Preferably, a zero sequence voltage gradient c is constructed in step 1dif(k) Comprises the following steps:
cdif(k)＝[u0-u0(k-1)]|/Δt
constructing a zero sequence voltage gradient sum E (k) as:
Figure BDA0003090564770000021
wherein K represents the current sampling point, Δ t represents the sampling interval, and takes ms as a unit, K represents the number of sampling points in a certain time window, and K is more than or equal to K.
Preferably, the zero sequence voltage gradient and the threshold value at start are set according to 15% of the amplitude of the rated phase voltage, i.e. the amplitude is 1.22kV, where K takes the threshold value Δ set of 3, 4, 5, 6 e (K) to be: 1.54(kV/ms)2、2.05(kV/ms)2、2.57(kV/ms)2、3.08(kV/ms)2。
Further, in step 4, the correlation coefficient ρ of the high and low frequency bands of the lineh、ρlIs composed of
Figure BDA0003090564770000022
Figure BDA0003090564770000031
The invention has the beneficial effects that:
(1) the invention analyzes the transient process of the fault by using the equivalent circuit which is suitable for the requirement of high-resistance grounding fault line selection, improves the accuracy of a line model when the fault occurs, and performs line selection by combining the voltage and current information on the high-frequency and low-frequency sections of the line.
(2) The fault detection algorithm is constructed by utilizing the sudden change of the zero sequence voltage, the problems that the protection device fails to work when a high-resistance grounding fault occurs and the traditional fault detection algorithm fails when the initial fault phase angle is small and the transition resistance is large are solved, and the starting time of the line selection device is greatly prolonged.
(3) The method and the device use the transient state information of the bus zero sequence voltage and the zero sequence current of each line in high and low frequency bands to select lines, and avoid the defects of failure information omission and low line selection accuracy rate caused by performing failure line selection only by using a single characteristic quantity.
(4) The fault information of each frequency band after the fault occurs can be fully utilized, the fault characteristics are amplified, the high-resistance grounding fault can be quickly responded, the adaptability is wide, and the fault line can be accurately selected under various extreme fault conditions.
Drawings
FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is a diagram of a conventional 15% start of rated phase voltage amplitude;
FIG. 3 is a zero sequence voltage gradient and start-up;
fig. 4 is a zero sequence network for a single phase earth fault;
FIG. 5 is a simplified zero sequence network;
FIG. 6 is a simulation model in the present embodiment;
fig. 7(a) is zero sequence current of the noiseless feeder in this embodiment;
fig. 7(b) is zero sequence voltage of the bus of the noiseless feeder line in this embodiment;
fig. 8(a) is zero sequence current of the feeding line containing noise in the present embodiment;
fig. 8(b) shows the zero sequence voltage of the bus of the feeder line containing noise in this embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described below clearly and completely, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the present invention provides a line selection method for a high-resistance ground fault based on line transient characteristics, which includes the following steps:
(1) according to the fault starting criterion, if E (k) > Δ EsetOr u0≥15％UmThen judging that the system has a fault, and collecting the zero sequence current i of the line with two power frequency periods by the system0k(n) and bus zero sequence voltage u0(n) where E (k) is the sum of zero sequence voltage gradients,. DELTA.EsetTo use the sum of zero-sequence voltage gradients asStarting threshold at start-up, u0Zero sequence voltage, U, of neutral pointmA nominal phase voltage amplitude.
(2) Extracting low-frequency components u of voltage and current by using filter0l(n) and i0l(n), high frequency component u0h(n) and i0h(n)。
u0l(n)、i0l(n)、u0h(n)、i0hAnd (n) the low-frequency zero-sequence voltage, the low-frequency zero-sequence current, the high-frequency zero-sequence voltage and the high-frequency zero-sequence current are respectively extracted by using a filter.
(3) Extracting the high and low frequency component data of the voltage and the current after the fault for correlation analysis to obtain the correlation coefficient rho of the corresponding high and low frequency bandsh、ρl. Where ρ ishAnd ρlRespectively as follows:
Figure BDA0003090564770000041
Figure BDA0003090564770000042
(4) solving the inverse correlation coefficient p of each linekAnd solving a fault line judgment matrix s, wherein lines corresponding to elements '-1' in the matrix s are fault feeders, if all the elements in s are '1', the lines are judged to be bus faults, and according to verification, a threshold value P of an inverse difference correlation coefficient is setset0.8, wherein:
Figure BDA0003090564770000043
Figure BDA0003090564770000044
the traditional fault line selection device judges whether a fault occurs by detecting whether the neutral point voltage exceeds a set value in a power frequency period, wherein the set value is generally 15% of a rated voltage amplitude. However, when the resonant grounding system is grounded with high resistance, the strength of the fault signal is weak, and the zero sequence voltage may be less than 15% of the phase voltage, which causes the failure of the starting method of the traditional line selection device. The zero sequence component appears after the system has a fault, zero sequence voltage with small amplitude exists in the system during normal operation only because three-phase parameters are not strictly symmetrical, and the zero sequence voltage is obviously increased after the fault, so that the zero sequence voltage can be used as an ideal starting amount for generating a high-resistance ground fault.
Constructing a zero sequence voltage gradient cdif(k) Is composed of
cdif(k)＝[u0(k)-u0(k-1)]/Δt (1)
Zero sequence voltage gradient and E (k) is
Figure BDA0003090564770000051
In the above equation, k denotes the current sample point, u0(k) And expressing zero sequence voltage under a K sampling point, delta t expresses a sampling interval, the unit of ms is adopted, K expresses the number of sampling points in a certain time window, and K is more than or equal to K.
Different fault types are set in the simulation model of the resonant grounding system shown in FIG. 6, and the starting time of the two starting methods is compared and analyzed. Suppose that in line L3And the tail end of the transformer generates an extreme fault condition of a small fault closing angle and different transition resistors.
The zero sequence voltage gradient and the starting threshold value used for starting can be set according to the setting value set for starting of the traditional line selection device, and the setting value is generally 15% of the rated phase voltage amplitude. By detecting whether the neutral point voltage exceeds a setting value (15% U)m) The start of the fault detection method of (2) is shown in fig. 2.
Starting zero-sequence voltage gradients and threshold values corresponding to different K values according to a conventional device, wherein the value of K is 5, and the starting result is shown in FIG. 3 by using the zero-sequence voltage break variable.
FIG. 4 is a zero sequence network for single phase earth fault, where Lk0lZero sequence inductance, R, for a unit length of k for a feed linek0lResistance per unit length, Ck0l、C'k0lCapacitors at two sides of the circuit; l isf0b(Lf0l)、Rf0b(Rf0l) And Cf0b(Cf0l)、Cf0l(C'f0l) The single-bit zero-sequence inductor, the resistor and the capacitors on two sides are respectively close to (far from) a bus end of a fault feeder line fault point.
When the power distribution network normally operates without faults, the impedance Z of the input end of the feeder lineocComprises the following steps:
Figure BDA0003090564770000052
in the formula, ZcWhich is the impedance characteristic of the line, gamma is the line propagation coefficient,
Figure BDA0003090564770000061
Figure BDA0003090564770000062
r, L, C is unit length resistance, inductance, and capacitance of the circuit; l is the length of the feed line,
Figure BDA0003090564770000063
and
Figure BDA0003090564770000064
respectively, feeder port voltage and current.
Neglecting the line resistance, when the power frequency angular frequency ω is 2 π f to substitute formula (3), the impedance Z of the input end of the feeder k in the zero sequence networkock(f) Is composed of
Figure BDA0003090564770000065
In the formula:
Figure BDA0003090564770000066
is a masterA zero-sequence voltage vector of the line,
Figure BDA0003090564770000067
a zero sequence current vector of a feeder line k; l is0k、C0kRespectively the zero sequence inductance and the distributed capacitance of the kth feeder line unit length lkIs the length of the feed line k, Lk＝L0klk，Ck＝C0klkRespectively a zero sequence inductance and a distributed capacitance on the whole feeder line k.
When in use
Figure BDA0003090564770000068
When Z isockThe feed line k resonates for the first time, 0.
Figure BDA0003090564770000069
When f is more than or equal to 0 and less than fkWhen the zero sequence impedance of the line k is capacitive; when f > fkWhen the zero sequence impedance of the line k is not unified any more, the frequency is higher than f when the line is selected by using the impedance characteristic of the linekWill not be suitable for faulty line selection.
If it is
Figure BDA00030905647700000610
When f is more than or equal to 0 and less than fminAll the lines are capacitive. Minimum resonance frequency f according to parameters of overhead and cable linesminThe value of (a) is large, typically in the thousands of hertz, and even tens of thousands of hertz.
Suppose that the feeder 2 has a single-phase earth fault in the zero-sequence network of the single-phase earth fault shown in fig. 4, and f is greater than or equal to 0 and less than f in the frequency bandminWhen the impedance of the input end of the sound feeder is
Figure BDA00030905647700000611
In formula (6): ck0Is a robust feeder equivalent lumped parameter capacitance.
The equivalent impedance of the fault feeder line is the impedance of all sound lines and arc suppression coils, namely the parallel impedance of the equivalent lumped parameter capacitor and one inductor of each feeder line. So that figure 4 can be simplified to that shown in figure 5.
Zero sequence equivalent admittance Y of fault feeder 22(f) Is composed of
Figure BDA00030905647700000612
In the formula (7), the reaction mixture is,
Figure BDA00030905647700000613
and
Figure BDA00030905647700000614
respectively feeder 2 port current and bus voltage,
Figure BDA00030905647700000615
is the phasor of the current flowing through the arc suppression coil,
Figure BDA0003090564770000071
is the zero sequence current phasor of the feeder line k, f is the power frequency, LpIs the arc suppression coil inductance of the power distribution network. When the frequency f is gradually increased from 0, the zero sequence impedance at the input end of the feeder line is changed from inductive to capacitive. When the zero sequence equivalent admittance Y of the feed line kk(f) When the value is 0, the system generates parallel resonance, and the resonance frequency is assumed to be fres. The compensation mode of the arc suppression coil is over-compensation generally, and the system inductive reactance is slightly larger than the zero sequence capacitive reactance of all the lines under the power frequency condition, so fresIs close to the power frequency, obviously fres＜＜fmin。
After the single-phase earth fault of the power distribution network occurs, f is more than 0 and less than fresWhen the fault feeder is sensitive; in frequency band fres＜f＜fminAnd meanwhile, the fault feeder is capacitive. The sound feeder is capacitive in the whole frequency band according to the formula (6). In summary, the invention will set 0 < fresThe frequency band is defined as the low frequency band, fres＜f＜fminThe frequency band in which the antenna is located is defined as a high frequency band.
If it is
Figure BDA0003090564770000072
Figure BDA0003090564770000073
In the above formula rhohAnd ρlHigh and low frequency band correlation coefficient u of voltage and current respectively0l(n)、i0l(n)、u0h(n)、i0hAnd (n) corresponding to the low-frequency zero-sequence voltage, the low-frequency zero-sequence current, the high-frequency zero-sequence voltage and the high-frequency zero-sequence current extracted by the filter.
Sound feeder rhohAnd rholBoth should be highly correlated and both should have a correlation coefficient | ρ | of greater than 0.8.
The impedance characteristic of the fault line is inductive in a low frequency section and capacitive in a high frequency section, and in the high frequency section, the zero sequence current mutation directions of the fault feeder line and the sound feeder line are opposite, the current amplitude of the fault feeder line is equal to the sum of the zero sequence current amplitudes of all the sound lines, and the relationship just reflects the kirchhoff current law. Therefore, ρ of the faulty lineh＝-1。
Correlation coefficient rho of fault line in low frequency bandlAs shown in equation (10).
Figure BDA0003090564770000074
Defining a reciprocal difference correlation coefficient pkComprises the following steps:
Figure BDA0003090564770000075
from the above analysis, p of the healthy lineh、ρlShould be highly correlated, the inverse correlation coefficient of the robust line is a value close to 0; as can be seen from equation (10), the correlation coefficient of the fault line in the low frequency band is at most 1, i.e., the correlation coefficient of the fault line is 1The inverse correlation coefficient is such that it is a value greater than 2.
According to simulation verification, a threshold value p of the inverse difference correlation coefficient is setset0.8. And defining a fault line discrimination matrix s as
Figure BDA0003090564770000081
And a line corresponding to the element "-1" in the matrix s is a fault feeder, and if the fault is determined according to the fault starting criterion and the elements in the matrix s are all '1', the bus fault is determined.
Example 1
A simulation model of a power distribution network of a 10kV resonance grounding system built by utilizing Matlab is shown in FIG. 6, wherein the system consists of 6 feeder lines and has 3 line models in total, wherein L1、L2、L3For overhead lines, L2、L6Is a cable line, L4For a wire-cable hybrid line, the model specific parameters are as follows:
a circuit: overhead line positive sequence parameter R1＝0.17Ω.km-1，L1＝1.2100mH.km-1，C1＝0.00969μF.km-1Zero sequence line positive sequence parameter R0＝0.23Ω.km-1，L0＝5.4780mH.km-1，C0＝0.00800μF.km-1. Cable line positive sequence parameter R11＝0.27Ω.km-1，L11＝0.2548mH.km-1，C11＝0.33910μF.km-1Zero sequence parameter R00＝2.70Ω.km-1，L00＝1.0191mH.km-1，C00＝0.28000μF.km-1. Transformer transformation ratio: 110KV/10KV, YN/d11 as connection group; the arc suppression coil is overcompensated, the compensation coefficient is 10%, and the sampling frequency of the system is 6 KHz.
Extracting low-frequency component u of voltage and current by filter0l(n) and i0l(n) and a high frequency component u0h(n) and i0h(n), the low frequency range is 0-60 Hz, and the high frequency range is 100-1000 Hz. If the system fails, according to the aboveIn the fault starting algorithm, the zero sequence voltage change gradient and/or the phase voltage 15% are higher than the set threshold value, the fault sampling device is started, and the zero sequence current and the bus zero sequence voltage of each feeder line after the fault are collected, and fig. 7(a) -7 (b) show the zero sequence current and the bus zero sequence voltage of the noiseless feeder line in the embodiment.
In order to verify the high-resistance grounding fault line selection method based on the transient characteristics of the line, verification is respectively carried out under different fault conditions; faults under different transition resistances, different fault closing angles and fault phases and noise backgrounds.
Different transition resistance
Different transition resistances are set, and other faults with consistent fault conditions are assumed to be in the circuit L in the simulation diagram of FIG. 61When a single-phase earth fault with an initial phase angle of 30 degrees at a position 10km away from the bus occurs, the simulation result is shown in table 1.
TABLE 1 line selection results at different transition resistances
Figure BDA0003090564770000082
Figure BDA0003090564770000091
As can be seen from Table 1, the proposed line selection method can accurately select the fault line within 0-3000 omega of the fault transition resistance, and has high sensitivity.
Different fault closing angles and fault phases
On the line L1And (3) generating a single-phase earth fault which is 10km away from the bus and has a transition resistance of 1000 omega, setting different fault closing angles and fault phases, keeping other fault conditions unchanged, and obtaining a line selection result shown in table 2.
TABLE 2 different fault closing angle, i.e. fault phase selection structure
Figure BDA0003090564770000092
As can be seen from Table 2, under the influence of different fault closing angles and fault phases, the proposed line selection method can still accurately select the fault line, is not influenced by the fault closing angles and the fault phases, and is high in line selection sensitivity and strong in reliability.
Different signal-to-noise ratios
Considering the influence of noise on a fault signal of a power distribution network in an actual operation environment, 30dB white Gaussian noise is added in simulation to verify the reliability of the line selection method, and the line selection result is shown in Table 3. DfIs the distance of the point of failure. Fig. 8(a) -8 (b) are current and voltage waveforms at 30dB signal-to-noise interference.
TABLE 3 noise and noise-free line selection results
Figure BDA0003090564770000093
Figure BDA0003090564770000101
Comparing table 3, it can be known that after 30dB of noise is added, the method can still accurately select the faulty line, and can also identify the bus fault, without being affected by the noise environment.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (4)

1. A high-resistance ground fault line selection method based on line transient characteristics is characterized by comprising the following steps:
step 1. Fault detection
Detecting neutral point voltage to construct zero sequence voltage change gradient, and setting corresponding starting threshold value by combining 15% of traditional phase voltage as the starting of fault;
step 2, analyzing the zero sequence impedance characteristic of each feeder line by using a fault equivalent circuit suitable for high-resistance grounding, and analyzing to obtain that after a fault occurs, the healthy feeder line is capacitive in high and low frequency bands, while the fault feeder line is capacitive in the high frequency band and inductive in the low frequency band;
and 3, extracting low-frequency and high-frequency components of the transient signal by using a low-pass filter and a band-pass filter, and selecting a fault line by using the difference of the zero-sequence current of the high-low frequency section feeder line and the zero-sequence voltage correlation coefficient of the bus.
2. The line transient characteristic-based high-resistance ground fault line selection method according to claim 1, wherein in step 1, the constructed zero-sequence voltage gradient cdif(k) Comprises the following steps:
cdif(k)＝[u0(k)-u0(k-1)]/Δt
zero sequence voltage gradient and E (k) is
Figure FDA0003090564760000011
Where k denotes the current sample point, u0(k) And expressing zero sequence voltage under a K sampling point, delta t expresses a sampling interval, the unit of ms is adopted, K expresses the number of sampling points in a certain time window, and K is more than or equal to K.
3. A high impedance ground fault line selection method based on line transient characteristics as claimed in claim 1, wherein in step 2, the minimum resonant frequency when resonance occurs is fmin：
Figure FDA0003090564760000012
Lk＝L0klk、Ck＝C0klk，L0k、C0kRespectively is zero sequence inductance and distributed capacitance l on the whole feeder line kkIs the feeder k length; minimum resonance frequency fminThe value of (a) is large, typically several kilohertz, even tens of kilohertz;
f is more than or equal to f in frequency band 0 after single-phase earth fault occursminIn time, the impedance at the input end of the healthy feeder line is:
Figure FDA0003090564760000013
in the formula:
Figure FDA0003090564760000014
and
Figure FDA0003090564760000015
according to the parameters of overhead line and cable line, Ck0Zero sequence equivalent admittance Y for a faulty feeder for a healthy feeder equivalent lumped parameter capacitance2(f) Comprises the following steps:
Figure FDA0003090564760000021
Figure FDA0003090564760000022
and
Figure FDA0003090564760000023
respectively feeder 2 port current and bus voltage,
Figure FDA0003090564760000024
is the phasor of the current flowing through the arc suppression coil,
Figure FDA0003090564760000025
is the zero sequence current phasor of the feeder line k, and f is the power frequencyFrequency, LpFor the inductance of the arc suppression coil of the power distribution network, when the frequency f is gradually increased from 0, the zero sequence impedance of the input end of the fault feeder line can be changed from inductive to capacitive, and when the zero sequence equivalent admittance Y of the fault feeder line k is changedk(f) When the value is 0, the system generates parallel resonance, and the resonance frequency is assumed to be fres；
When the single-phase earth fault occurs in the power distribution network, f is more than 0 and less than fresWhen the fault feeder is sensitive, in the frequency band fres＜f＜fminMeanwhile, the fault feeder is capacitive; the sound feeder line is capacitive in the whole frequency band and is defined as 0 < fresIs a low frequency band, fres＜f＜fminIs a high frequency band.
4. The line transient characteristic-based high-resistance ground fault line selection method according to claim 1, wherein in the step 3, the high-frequency-band relation number p of the voltage and the current ish、ρlIs composed of
Figure FDA0003090564760000026
Figure FDA0003090564760000027
Wherein u is0l(n)、i0l(n)、u0h(n)、i0h(n) the low-frequency zero-sequence voltage, the low-frequency zero-sequence current, the high-frequency zero-sequence voltage and the high-frequency zero-sequence current are respectively extracted by a filter;
the impedance characteristic of the sound feeder line in the whole frequency band is capacitive, so that the current of the sound feeder line in the whole frequency band is in direct proportion to the voltage derivative, and the sound feeder line rhohAnd rholBoth should be highly correlated, and both should have correlation coefficients | ρ | values greater than 0.8;
high-low frequency band correlation coefficient rho of fault feeder lineh-1; when analyzing the current and voltage waveform correlation coefficient of the fault feeder line in the low frequency band, the fault initial phase angle is consideredThe influence of the direct current component of theta which is not attenuated simultaneously on voltage and current waveforms is respectively analyzed on the correlation coefficients under different fault initial phase angles, and the correlation coefficient rho of the fault line under the low frequency bandlThe range of (A) is as follows:
Figure FDA0003090564760000031
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