CN108199356B - Wave-front information-based DC transmission line ultra-high speed protection method - Google Patents

Wave-front information-based DC transmission line ultra-high speed protection method Download PDF

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CN108199356B
CN108199356B CN201711487275.2A CN201711487275A CN108199356B CN 108199356 B CN108199356 B CN 108199356B CN 201711487275 A CN201711487275 A CN 201711487275A CN 108199356 B CN108199356 B CN 108199356B
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fault
protection
current
zero
transmission line
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CN108199356A (en
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宋国兵
张晨浩
王莉
樊占峰
李佳朋
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Xuji Group Co Ltd
Xian Jiaotong University
Xuchang XJ Software Technology Co Ltd
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Xuji Group Co Ltd
Xian Jiaotong University
Xuchang XJ Software Technology Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/265—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured making use of travelling wave theory
    • 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
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Locating Faults (AREA)

Abstract

The invention discloses a wave-front information-based DC transmission line ultra-high speed protection method, which comprises the following steps: 1) measuring the current at the protective installation position of the head end of the line, and calculating the zero-modulus component of the current; 2) identifying the rising edge part of the traveling wave so as to start protection to judge the fault; 3) and after the protection is started, calculating fault sampling data, and judging the fault sampling data into an intra-area fault and an extra-area fault. The invention has high transition resistance and direction discrimination capability while extracting the wavefront fault distance information; the method has the advantages of rapidity, reliability, long protection range and no high sampling rate requirement.

Description

Wave-front information-based DC transmission line ultra-high speed protection method
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a direct-current transmission line ultra-high speed protection method based on wavefront information.
Background
The direct current transmission has the advantages of high transmission capacity, flexible power control, long-distance transmission and the like, and the conventional direct current and the flexible direct current are widely applied in the current power transmission of the power system. After a direct current line fails, the shorter the fault duration is, the better the transmission power of a transmission line is improved and the transient stability of a power system is enhanced, the requirement of flexible direct current transmission of Zhang Bei for 3ms on the relay protection exit time is provided, and ultra-high speed protection based on the initial moment of the fault becomes the key point of the current research.
The traveling wave protection has the characteristic of quick action, and different protection schemes of the line are given mainly by utilizing the traveling characteristics (the relation between the wave speed, the propagation time and the fault distance) of fault traveling waves and the wave characteristics (the slope and the sudden change of the fault traveling waves) of the traveling waves. However, the existing protection principle utilizing the traveling characteristic of fault traveling waves has the problems of high sampling rate requirement and mathematical theory defect; the protection principle utilizing the fault traveling wave characteristic has the problem of lightning misoperation, and the sensitivity of the protection principle is influenced by transition resistance, fault distance and sampling frequency.
Disclosure of Invention
The invention aims to provide a wave-front information-based direct-current transmission line ultra-high-speed protection method to solve the technical problem. The front edge of the fault traveling wave is called a wave front, and the wave front contains rich fault information; the invention improves the performance of the existing traveling wave protection and meets the requirement of a direct current circuit on relay protection. According to the method, theoretical analysis and simulation are firstly carried out to obtain the conclusion that when the parameter frequency change characteristic of a line and the broadband characteristic of a fault are taken into consideration, the change degree of the wave front shape of the fault traveling wave is related to the fault distance, and the transition resistance only affects the wave front amplitude and does not affect the change degree of the wave front. Therefore, a correlation coefficient is constructed to reflect the similarity degree between the traveling wave fronts of two different fault distances, and the fault discrimination is realized. The correlation coefficient calculation of the wave front needs to sample data in T time of the traveling wave front, so that the arrival time of the traveling wave front needs to be identified, and the relative variation of the zero-mode current before and after time is calculated by using a ratio method, so that the identification of the rising edge part (wave front) of the traveling wave is realized.
The protection method provided by the invention utilizes the fault information contained in the traveling wave front edge, eliminates the influence of the change of the fault traveling wave front amplitude by utilizing the correlation coefficient, only simply reflects the similarity degree of each unit change between the fault traveling wave front edge and the correlation reference, extracts the front fault distance information and has high transition resistance capability and direction discrimination capability. The method has the advantages of rapidity, reliability and no high sampling rate requirement.
In order to achieve the purpose, the invention adopts the following technical scheme:
the direct-current transmission line ultra-high speed protection method based on the wave front information comprises the following steps:
1) measuring the current at the protective installation position of the head end of the line, and calculating the zero-modulus component of the current;
2) identifying the rising edge part of the traveling wave so as to start protection to judge the fault;
3) and after the protection is started, calculating fault sampling data, and judging the fault sampling data into an intra-area fault and an extra-area fault.
Further, in step 1): measuring the current at the protection installation position of the head end of the direct current transmission line, and calculating the current zero-modulus component according to the following formula;
Figure BDA0001534993320000021
wherein, Ip、In、I0、I1Respectively the measured positive and negative currents at the protection installation position and the calculated zero-mode and one-mode currents.
Further, in step 2): identifying the rising edge part of the traveling wave according to the formula (2), thereby starting protection to judge the fault;
Figure BDA0001534993320000022
wherein i0(n)、i0(n+1)、i0(n+2)、i0(n +3) is a zero-mode current sampling value, kset、k1set、k2set、k3setAs a setting value, the following conditions are met:
Figure BDA0001534993320000023
in the formula k1Is the ratio of the front and back moments of the zero-mode current in the normal working process of the circuit, Krel1、Krel2、Krel3For reliable coefficients, the three values increase in sequence.
Further, Krel1、Krel2、Krel3Respectively taking 1.1, 1.3 and 1.5.
Further, in step 3): after protection is started, calculating fault sampling data according to the formula (4):
Figure BDA0001534993320000031
where T is the data length used for protection discrimination, TsFor the sampling step size, i0set(j) Sampling values in a T time period of the metallic fault zero-mode current traveling wave front near the midpoint of the line; i.e. i0(j) A zero mode current sampling value measured for protection;
when rho is more than or equal to rhosetJudging the fault in the area, and performing protection action, otherwise, judging the fault outside the area, wherein:
ρ≥ρset＝Krelρ1 (5)
where rho1The correlation coefficient K is calculated by the formula (4) when the outer side of the direct current filter and the smoothing reactor at the tail end of the direct current line has a faultrelIs a reliability factor.
Further, KrelFor the reliability factor, 1.1 was taken.
Compared with the prior art, the invention has the following beneficial effects:
the invention utilizes the fault information contained in the front edge of the traveling wave, eliminates the influence of the amplitude change of the front edge of the fault traveling wave by utilizing the correlation coefficient, only simply reflects the similarity degree of each unit change between the front edge of the fault traveling wave and the correlation reference, extracts the front fault distance information and simultaneously has high transition resistance capability and direction discrimination capability. The method has the advantages of rapidity, reliability (no influence of lightning stroke and operation disturbance) and no high sampling rate requirement.
Drawings
FIG. 1 shows the frequency characteristics of the resistance, inductance and capacitance modulus per unit length of a transmission line; wherein FIG. 1(a) is a graph showing the variation of mode resistance with frequency; wherein FIG. 1(b) is the variation of the mode inductance with frequency; wherein FIG. 1(c) is a graph of mode capacitance as a function of frequency;
FIG. 2 is a transmission line propagation coefficient frequency characteristic; wherein fig. 2(a) is an attenuation coefficient frequency characteristic; wherein fig. 2(b) is a phase shift coefficient frequency characteristic;
FIG. 3 is a frequency characteristic of a transmission line wave velocity;
FIG. 4 is a fault current characteristic; wherein fig. 4(a) is fault current; where FIG. 4(b) is fault zero mode current;
FIG. 5 is a relationship between a fault traveling wave front and a fault distance;
FIG. 6 is a relationship between a traveling wave front and a transition resistance;
FIG. 7 is a block diagram of a DC power transmission system;
FIG. 8 is a flow chart of a method of ultra-high speed protection based on wavefront information.
Detailed Description
The invention will be further described with reference to the accompanying drawings in which:
the invention analyzes the frequency variation characteristic of the transmission line parameters and obtains the line propagation coefficient and wave velocity characteristic considering the influence of each line parameter along with the frequency variation. FIG. 1 shows the frequency characteristics of the resistance, inductance and capacitance modulus per unit length of a transmission line; FIG. 2 is a transmission line propagation coefficient frequency characteristic; fig. 3 is a frequency characteristic of a transmission line wave velocity. It can be seen that: signals of different frequencies propagate at different speeds on the transmission line and are attenuated differently during propagation. The difference of the parameters of the transmission line between low frequency and high frequency causes the difference of the propagation characteristics of signals with different frequencies in the line.
Based on the above conclusion, the fault information contained in the fault traveling wave is analyzed by combining the broadband characteristic of the fault point traveling wave. FIG. 4 is a fault current characteristic, and FIG. 5 is a fault traveling wave front versus fault distance; fig. 6 shows the relationship between the traveling wave front and the transition resistance. And the following conclusions are reached:
1) the degree of change in the shape of the wavefront of the fault traveling wave is related to the distance to the fault.
2) The transition resistance only affects the amplitude of the wave front and does not affect the degree of change of the wave front.
Referring to fig. 1 to 8, the present invention provides a method for ultra-high speed protection of a dc transmission line based on wavefront information, comprising the following steps:
1) measuring the current at the protection installation position of the head end of the direct current transmission line, and calculating the current zero-modulus component according to the following formula;
Figure BDA0001534993320000051
wherein, Ip、In、I0、I1Respectively the measured positive and negative currents at the protection installation position and the calculated zero-mode and one-mode currents.
2) Identifying the rising edge part (wave front) of the traveling wave according to the formula (2), thereby starting protection to judge the fault; the protection is started according to the formula (2), otherwise, the protection is not started;
Figure BDA0001534993320000052
wherein i0(n)、i0(n+1)、i0(n+2)、i0(n +3) is a zero-mode current sampling value, kset、k1set、k2set、k3setAs a setting value, the following conditions are met:
Figure BDA0001534993320000053
in the formula k1Is the ratio of the front and back moments of the zero-mode current in the normal working process of the circuit, Krel1、Krel2、Krel3For reliable coefficients, three values are required to be increased in sequence, and the method is respectively 1.1, 1.3 and 1.5.
Aiming at the problem that the ratio of front time to rear time is infinite due to zero-mode current flowing through zero point, a calculation threshold k is setsetAnd eliminating the influence of zero crossing points.
3) After protection is started, calculating fault sampling data according to the formula (4):
Figure BDA0001534993320000054
where T is the data length used for protection discrimination, TsFor the sampling step size, i0set(j) Calculating a reference for a correlation coefficient for a sampling value in a T time period of the wave front of the zero-mode current traveling wave with metallic fault near the midpoint of the line; i.e. i0(j) To protect the measured zero mode current sample values.
When rho is more than or equal to rhosetJudging the fault in the area, and performing protection action, otherwise, judging the fault outside the area, wherein:
ρ≥ρset＝Krelρ1 (5)
where rho1The correlation coefficient K is calculated by the formula (4) when the outer side of the direct current filter and the smoothing reactor at the tail end of the direct current line has a faultrelFor the reliability factor, the invention takes 1.1.
Simulation verification:
fig. 7 is a diagram of a dc power transmission system. The invention takes a cloud wide +/-800 kV ultra-high voltage direct current transmission line as an example, and carries out simulation verification on the wave front information-based ultra-high speed protection method, wherein the sampling frequency is 20 kHz. The reference of the correlation coefficient is a sampling value rho in a 1.5ms time period of a metallic monopole fault zero-mode current traveling wave front at a position 800km away from the head end of a direct-current linesetIs 0.9319, k1Is 1, ksetIs 8.0X 10-4kA。
The protection results of the lines at different distances and in the case of transition resistance faults are shown in tables 1, 2, 3 and 4. In table f2、f3For line-end DC filters, smoothing reactors, outside faults, f8And N is the sampling point serial number for the lightning stroke disturbance of the direct current line.
It can be seen that the protection starts correctly when the dc line fails. Under the protection setting value, the non-direct-current line fault protection does not act; the fault protection range on the direct current line is about 200km-1400km away from the head end of the line. The protection can correctly distinguish direct current line faults and lightning stroke disturbance. Table 5 gives the relative rates of change of the correlation coefficients for metallic faults and 500 Ω transition resistance faults at different fault distances. With the increase of the distance between the fault and the relevant reference fault, the relative change rate brought by the transition resistance is larger, but is less than 2%, so that the protection principle provided by the invention is basically not influenced by the transition resistance.
In summary, the proposed protection principle works.
TABLE 1 line different distance fault correlation coefficient (0 omega transition resistance)
Figure BDA0001534993320000061
TABLE 2 line different distance fault correlation coefficient (100 omega transition resistance)
Figure BDA0001534993320000071
TABLE 3 line different distance fault correlation coefficient (300 omega transition resistance)
Figure BDA0001534993320000072
TABLE 4 line different distance fault correlation coefficient (500. omega. transition resistance)
Figure BDA0001534993320000073
TABLE 5 relative rates of change of correlation coefficients for metallic failures and 500 Ω transition resistance failures at different failure distances
Figure BDA0001534993320000074

Claims (5)

1. The direct-current transmission line ultra-high speed protection method based on the wave front information is characterized by comprising the following steps of:
1) measuring the current at the protective installation position of the head end of the line, and calculating the zero-modulus component of the current;
2) identifying the rising edge part of the traveling wave so as to start protection to judge the fault;
3) after protection is started, calculating fault sampling data, and judging the fault sampling data to be an intra-area fault and an extra-area fault;
in step 3): after protection is started, calculating fault sampling data according to the formula (4):
Figure FDA0002660668350000011
where T is the data length used for protection discrimination, TsFor the sampling step size, i0set(j) Sampling values in a T time period of the metallic fault zero-mode current traveling wave front near the midpoint of the line; i.e. i0(j) A zero mode current sampling value measured for protection;
when rho is more than or equal to rhosetJudging the fault in the area, and performing protection action, otherwise, judging the fault outside the area, wherein:
ρ≥ρset＝Krelρ1 (5)
where rho1The correlation coefficient K is calculated by the formula (4) when the outer side of the direct current filter and the smoothing reactor at the tail end of the direct current line has a faultrelIs a reliability factor.
2. The method for ultra-high speed protection of the direct current transmission line based on the wavefront information according to claim 1, wherein in the step 1): measuring the current at the protection installation position of the head end of the direct current transmission line, and calculating the current zero-modulus component according to the following formula;
Figure FDA0002660668350000012
wherein, Ip、In、I0、I1Respectively the measured positive and negative currents at the protection installation position and the calculated zero-mode and one-mode currents.
3. The method for ultra-high speed protection of the direct current transmission line based on the wavefront information according to claim 1, wherein in the step 2): identifying the rising edge part of the traveling wave according to the formula (2), thereby starting protection to judge the fault;
Figure FDA0002660668350000013
wherein i0(n)、i0(n+1)、i0(n+2)、i0(n +3) is a zero-mode current sampling value, kset、k1set、k2set、k3setAs a setting value, the following conditions are met:
Figure FDA0002660668350000021
in the formula k1Is the ratio of the front and back moments of the zero-mode current in the normal working process of the circuit, Krel1、Krel2、Krel3For reliable coefficients, the three values increase in sequence.
4. The method of claim 3, wherein K is Krel1、Krel2、Krel3Respectively taking 1.1, 1.3 and 1.5.
5. The method for ultra-high speed protection of direct current transmission line based on wave front information according to claim 1, wherein K isrelFor the reliability factor, 1.1 was taken.
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CN109193578B (en) * 2018-08-13 2020-03-13 西安交通大学 Rapid protection method for direct-current transmission line based on wave-front generalized Logistic function fitting
CN110133433B (en) * 2019-03-27 2021-07-06 国网浙江省电力有限公司电力科学研究院 Direct-current power distribution network fault disturbance identification method based on mutation integral product
CN110470952A (en) * 2019-08-19 2019-11-19 西安交通大学 The fault detection method of DC distribution net
CN111157843B (en) * 2020-01-06 2022-04-12 长沙理工大学 Power distribution network line selection method based on time-frequency domain traveling wave information

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