CN106841921B - Direct-current power distribution network line single-pole grounding fault positioning method - Google Patents

Direct-current power distribution network line single-pole grounding fault positioning method Download PDF

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CN106841921B
CN106841921B CN201710073697.9A CN201710073697A CN106841921B CN 106841921 B CN106841921 B CN 106841921B CN 201710073697 A CN201710073697 A CN 201710073697A CN 106841921 B CN106841921 B CN 106841921B
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吴在军
高仁栋
范文超
窦晓波
胡敏强
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Southeast 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
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections

Abstract

The invention discloses a method for positioning a single-pole ground fault of a direct-current power distribution network line, which comprises the following steps: 1) obtaining a fault current differential initial value expression according to a transient characteristic equation of the fault current; 2) replacing the differential initial value of the fault current by using an interpolation algorithm; 3) obtaining a fault location value expression containing a fault current differential initial value; 4) combining the fault location value expression with a loop current equation to obtain a fault location-based equation; 5) acquiring information of voltage and current values before and after the occurrence of the single-pole ground fault, and combining the fault current differential initial value obtained in the step 2) and the fault positioning equation obtained in the step 4) to obtain a fault positioning value. The method has the advantages of simple calculation, wide application range, no influence of factors such as transition resistance and the like, capability of realizing off-line maintenance and automatic operation, strong transition resistance tolerance, and high positioning precision when the transition resistance is increased.

Description

Direct-current power distribution network line single-pole grounding fault positioning method
Technical Field
The invention relates to the field of direct-current power distribution network line unipolar ground fault positioning, in particular to a direct-current power distribution network line unipolar ground fault positioning method based on an analysis method and applicable to a two-level Voltage Source Converter (VSC).
Background
Due to aging and damage of the line, the fault probability of the line is the largest compared with other parts in the direct current power distribution system. At present, related researches on fault location of a direct current power distribution system are few, and a direct current power transmission system with a relatively mature fault location technology is mainly used for reference. The line fault positioning method of the direct current transmission system mainly comprises an impedance method, a traveling wave method, a fault analysis method and the like. The impedance method is not ideal for practical engineering applications because it is greatly affected by ground resistance, line type, system parameters, and other factors. The traveling wave method is simple in principle, high in accuracy, not affected by line types and fault types, and more in practical engineering application, but when transition resistance exists and the amplitude of the traveling wave head is limited, the initial point of the wave head is more difficult to calibrate accurately, the positioning accuracy and reliability are seriously affected, and as the transition resistance continues to increase, the traveling wave fault positioning method cannot position faults due to no starting. The fault analysis method mainly utilizes the recording data of the fault recorder to carry out analysis and calculation, thereby achieving the purpose of distance measurement and positioning, can directly utilize the recording data of the fault recorder to realize fault positioning, has low requirements on the sampling rate of equipment and higher reliability, is established on an accurate line parameter model, and can influence the precision of fault positioning when the line parameter model is not accurate or the frequency variation characteristic is changed. More than 80% of fault types in the direct-current power distribution network are single-pole ground faults, so that the study of a fault positioning method of the single-pole ground fault types is very important.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a direct-current power distribution network line fault positioning method which is high in precision, convenient to operate and strong in transition resistance tolerance.
The technical scheme is as follows: the invention provides a VSC-based direct current power distribution network line monopole earth fault positioning method, which comprises the following steps:
1) obtaining a fault current differential initial value expression according to a transient characteristic equation of current under the conditions of underdamping and over-damping when a single-pole ground fault occurs in a VSC-based direct-current power distribution network line;
2) replacing the differential initial value of the fault current by using an interpolation algorithm according to the differential initial value expression of the fault current;
3) acquiring a fault positioning value expression containing a fault current differential initial value according to the fault current differential initial value expression;
4) combining the fault location value expression obtained in the step 3) with a loop current equation to obtain a fault location equation when a single-pole ground fault occurs in the VSC-based direct-current power distribution network line;
5) acquiring information of voltage and current values before and after the occurrence of the single-pole ground fault, and combining the fault current differential initial value obtained in the step 2) and the fault positioning equation obtained in the step 4) to obtain a fault positioning value.
In step 1), the differential initial value expression of the fault current is as follows:
Figure GDA0002212622370000021
vc(0) is the DC voltage before failure, iL(0) Is a dc current before failure, R ═ Req+Rf，L＝LeqR and L are total inductance and total resistance from the DC side outlet to the fault point on the positive and negative lines, respectively, RfIs transition resistance, ReqAnd LeqThe line resistance and inductance from the DC side outlet to the fault point on the positive and negative lines.
In step 2), the method for replacing the fault current differential initial value by using an interpolation algorithm comprises the following steps:
at t ═ 0+At the moment of time, the time of day,
Figure GDA0002212622370000022
a maximum value is taken and, therefore,
Figure GDA0002212622370000023
i (t) is a current sample value at time t, and i (Δ t + t) is a current sample value after a sampling interval Δ t.
In step 3), the fault location value expression containing the fault current differential initial value is as follows:
Figure GDA0002212622370000024
in the formula (3), RuAnd LuRespectively the resistance and inductance of a unit line length, x is a fault location value, and k is a fault current differential initial value.
In step 4), the loop current equation is:
Figure GDA0002212622370000025
combining the fault location value expression obtained in the step 3) with a loop current equation to obtain a fault location equation when the direct-current power distribution network line based on VSC has a single-pole earth fault:
Figure GDA0002212622370000031
U’dcis a direct current side direct current voltage.
And 5), acquiring the information of the voltage and the current before and after the occurrence of the single-pole ground fault, and analyzing by extracting the recording waveforms of the voltage and the current before and after the occurrence of the single-pole ground fault.
Has the advantages that: compared with the prior art, the invention has the following advantages:
(1) the method solves the current differential initial value based on the analytic method, realizes the fault location of the single-pole grounding fault of the direct-current power distribution network line, and has simple calculation and higher precision;
(2) compared with a traveling wave method, the method does not need to perform traveling wave injection positioning or tracking prediction positioning, so that the method is not influenced by factors such as transition resistance and the like, the calculation result can be used for off-line maintenance, and automatic operation can be realized;
(3) the device has strong capability of tolerating transition resistance, and still has high positioning precision when the transition resistance is increased;
(4) the interpolation algorithm is used for improving the traditional differential method instead of differentiation, the required sampling frequency is greatly reduced, and the accuracy requirement of the algorithm can be met when the sampling frequency is between 10kHz and 20 kHz;
(5) the invention is suitable for a single-end radiation type direct current distribution network, a ship direct current distribution system and a direct current transmission system with the power transmission having the dispersibility, the miniaturization and the randomness, and has wider application range.
Drawings
FIG. 1 is a single pole ground fault schematic;
FIG. 2 is a single pole ground fault equivalent circuit;
FIG. 3 is a flow chart of the algorithm of the present invention.
Detailed Description
A line single-pole grounding fault positioning method applicable to a VSC-based direct-current power distribution network comprises the following steps.
1) According to a transient characteristic equation of current under damping and over damping when a single-pole ground fault occurs in a direct-current power distribution network line based on a two-level Voltage Source Converter (VSC), a fault current differential initial value expression is obtained.
When a single-pole ground fault occurs on the direct-current side circuit of the VSC rectifier, the rapid discharging process of the capacitor is also experienced. As shown in fig. 1, when a single-pole ground fault occurs, the dc-side capacitor, the fault line and the transition resistor form a second-order RLC oscillation circuit due to the fact that the neutral point of the dc-side capacitor is equipotential with ground, so that the capacitor is rapidly discharged, and the oscillation form is related to the fault distance and the size of the transition resistor. Generally, when a single-pole ground fault occurs, low/high impedance may occur. When in use
Figure GDA0002212622370000041
In the process of underdamped discharge, the capacitor discharge loop generates an oscillation process, but the oscillation amplitude is smaller and smaller; when in use
Figure GDA0002212622370000042
In time, the fault loop transient energy will drop rapidly until it is zero for an over-damped discharge process. A single pole ground fault equivalent circuit is shown in figure 2.
When the transition resistance is small, in the case of underdamped discharge conditions, i.e. when
Figure GDA0002212622370000043
The transient characteristic equation of the current is:
Figure GDA0002212622370000044
in the formula (6), vc(0) And iL(0) Is a DC voltage current before failure, R ═ Req+Rf，L＝LeqR and L are total inductance and total resistance from the DC side outlet to the fault point on the positive and negative lines, respectively, RfIs transition resistance, ReqAnd LeqThe line resistance and inductance from the outlet of the DC side to the fault point on the positive and negative lines, C is the equivalent capacitance of the DC side,
Figure GDA0002212622370000045
β＝arctan(ω/δ)；
the current differential equation at this time is:
Figure GDA0002212622370000046
since the capacitor discharge phase i (t) is a convex function, there are:
Figure GDA0002212622370000047
thus, it can be seen that
Figure GDA0002212622370000048
The capacitance is monotonically decreased in the discharging stage, that is, the maximum value is obtained at the time when t is 0 +. At time t equal to 0+, the value of the current differential is:
Figure GDA0002212622370000049
wherein
Figure GDA00022126223700000410
Figure GDA00022126223700000411
Then
Figure GDA00022126223700000412
When the transition resistance is large, i.e. in an over-damped condition, i.e. when
Figure GDA0002212622370000051
The transient characteristic equation of the current is:
Figure GDA0002212622370000052
in the formula (I), the compound is shown in the specification,
Figure GDA0002212622370000053
at this time, the current is divided into:
Figure GDA0002212622370000054
at t ═ 0+At the instant, the value of the current differential is:
Figure GDA0002212622370000055
from the above, p1、p2At t is 0+At the instant, the value of the current differential is:
Figure GDA0002212622370000056
from the above analysis, the initial value of the current differential of the unipolar fault, whether under-damped or over-damped, can be represented by equation (1).
2) And replacing the fault current differential initial value by utilizing an interpolation algorithm according to the fault current differential initial value expression.
The traditional difference method is improved by an interpolation algorithm:
from the analysis in step 1), t is 0+At the moment of time, the time of day,
Figure GDA0002212622370000057
get the maximum value, then have
Figure GDA0002212622370000058
i (t) is a sampled value at time t, and i (Δ t + t) is a current sampled value after a sampling interval Δ t.
The interpolation algorithm is used for improving the traditional difference method, and the problems that the differential method replaces differential values and requires high sampling frequency and large errors are solved.
3) And acquiring a fault location value expression containing a fault current differential initial value according to the fault current differential initial value expression.
From the analysis of step 1), it can be known that the initial value of the current differential of the unipolar ground fault can be represented by formula (1) in both the underdamping and the overdamping processes.
Let x be the fault location value, then R ═ x Ru+Rf，L＝x*Lu。
Therefore, the fault location value expression of the single-pole ground fault represented by the fault current differential initial value k is as follows:
Figure GDA0002212622370000061
in the formula, RuAnd LuRespectively, the resistance and inductance parameters per unit cable length.
4) And combining the fault location value expression with the loop current equation to obtain a fault location equation when the VSC-based direct-current power distribution network line has the unipolar earth fault so as to solve the problem of transition resistance of the unipolar earth fault location equation.
The kirchhoff voltage equation of the circuit when the single pole is grounded is as follows:
Figure GDA0002212622370000062
therefore, combining equation (3) with equation (4), the fault location equation can be obtained as follows:
Figure GDA0002212622370000063
wherein, U'dcIs a direct current side direct current voltage.
The fault location equation (5) is obtained by combining a fault location value expression containing a fault current differential initial value and a loop equation, so that the influence of the transition resistance on fault location is eliminated.
5) Acquiring information of voltage and current values before and after the occurrence of the single-pole ground fault, and combining the fault current differential initial value obtained in the step 2) and the fault positioning equation obtained in the step 4) to obtain a fault positioning value.
The acquisition of the voltage and current value information before and after the occurrence of the single-pole ground fault is realized by extracting the voltage and current recording waveforms before and after the occurrence of the single-pole ground fault and analyzing.
Fig. 3 is a flowchart of an algorithm of a method for positioning a single-pole ground fault of a line of a VSC-based direct-current power distribution network according to the present invention. Firstly, obtaining current and voltage information before and after a fault by extracting voltage and current recording waveforms before and after the occurrence of the single-pole ground fault, wherein the current and voltage information comprises direct current voltage and current value v before the faultc(0)，iL(0). Then, an interpolation type substitution equation of the current differential initial value k can be obtained by using the formula (2), an interpolation type substitution equation of the current differential di/dt can be obtained in the same way, and finally, a fault location value can be obtained by substituting the current differential di/dt into the fault location equation (5).

Claims (6)

1. A VSC-based direct current power distribution network line unipolar earth fault positioning method is characterized by comprising the following steps:
1) obtaining a fault current differential initial value expression according to a transient characteristic equation of current under the conditions of underdamping and over-damping when a single-pole ground fault occurs in a VSC-based direct-current power distribution network line;
2) replacing the differential initial value of the fault current by using an interpolation algorithm according to the differential initial value expression of the fault current;
3) acquiring a fault positioning value expression containing a fault current differential initial value according to the fault current differential initial value expression;
4) combining the fault location value expression obtained in the step 3) with a loop current equation to obtain a fault location equation when a single-pole ground fault occurs in the VSC-based direct-current power distribution network line;
5) acquiring information of voltage and current values before and after the occurrence of the single-pole ground fault, and combining the fault current differential initial value obtained in the step 2) and the fault positioning equation obtained in the step 4) to obtain a fault positioning value.
2. The method according to claim 1, wherein in step 1), the fault current differential initial value expression is as follows:
Figure FDA0002212622360000011
vc(0) is the DC voltage before failure, iL(0) Is a dc current before failure, R ═ Req+Rf，L＝LeqR and L are total inductance and total resistance from the DC side outlet to the fault point on the positive and negative lines, respectively, RfIs transition resistance, ReqAnd LeqThe line resistance and inductance from the DC side outlet to the fault point on the positive and negative lines.
3. The method according to claim 2, wherein in step 2), the method for replacing the fault current differential initial value by using the interpolation algorithm is as follows:
at t ═ 0+At the moment of time, the time of day,
Figure FDA0002212622360000012
a maximum value is taken and, therefore,
Figure FDA0002212622360000013
i (t) is a current sample value at time t, and i (Δ t + t) is a current sample value after a sampling interval Δ t.
4. The method according to claim 3, wherein in step 3), the fault location value expression containing the initial value of the fault current differential is as follows:
Figure FDA0002212622360000021
in the formula (3), RuAnd LuRespectively the resistance and inductance of a unit line length, x is a fault location value, and k is a fault current differential initial value.
5. The method according to any one of claims 1 to 4, wherein in step 4), the loop current equation is:
Figure FDA0002212622360000022
combining the fault location value expression obtained in the step 3) with a loop current equation to obtain a fault location equation when the direct-current power distribution network line based on VSC has a single-pole earth fault:
Figure FDA0002212622360000023
x is a fault location value, k is an initial fault current differential value, vc(0) Is the DC voltage before failure, iL(0) Is a direct current before failure, RuAnd LuResistance and inductance, R, respectively, per unit line lengthfIs transition resistance, U'dcIs a direct current side direct current voltage.
6. The method according to any one of claims 1 to 4, wherein in the step 5), the obtaining of the voltage and current value information before and after the occurrence of the single-pole ground fault is performed by extracting and analyzing voltage and current waveform records before and after the occurrence of the single-pole ground fault.
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CN107589344A (en) * 2017-09-15 2018-01-16 广西电网有限责任公司电力科学研究院 A kind of low-voltage power line Fault Locating Method based on probe current frequency analysis
CN108919053A (en) * 2018-06-25 2018-11-30 华北电力大学 A kind of flexible direct current microgrid Fault Locating Method
CN108957245B (en) * 2018-09-26 2020-09-01 北京四方继保自动化股份有限公司 Flexible direct-current power distribution network single-pole fault identification method based on full fault current
CN110161369A (en) * 2019-04-11 2019-08-23 华北电力大学 A kind of bipolar short trouble localization method of DC grid based on overhead transmission line RL model
CN110018401B (en) * 2019-05-20 2021-03-16 国网甘肃省电力公司天水供电公司 Distribution line single-phase earth fault positioning method
CN110323726B (en) * 2019-07-17 2021-05-14 国网江苏省电力有限公司 Self-adaptive line protection method and device for direct-current power distribution network
CN110350500B (en) * 2019-08-13 2021-08-27 南京南瑞继保电气有限公司 Method, device, system, equipment and medium for protecting pseudo bipolar direct current distribution network
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