CN109327017B - Hybrid line distance protection method based on lossless line equation - Google Patents

Hybrid line distance protection method based on lossless line equation Download PDF

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CN109327017B
CN109327017B CN201811353800.6A CN201811353800A CN109327017B CN 109327017 B CN109327017 B CN 109327017B CN 201811353800 A CN201811353800 A CN 201811353800A CN 109327017 B CN109327017 B CN 109327017B
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line
lossless
voltage
gil
reactance
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CN109327017A (en
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李博通
谷天峰
李斌
陈晓龙
陈冲
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HARBIN COSLIGHT ELECTRIC AUTOMATION Co.,Ltd.
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Tianjin University
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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
    • 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
    • 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

Abstract

The invention relates to a mixed line distance protection method based on a lossless line equation, which comprises the following steps: based on the frequency domain parameters of the power transmission line, obtaining a measured reactance expression of the lossless line part when the line has different types of faults according to the transmission equation of the lossless line part of the power transmission line; according to the pure reactance characteristic presented by the lossless part of the power transmission line, making a phasor diagram of voltage and current at the protective installation position, solving the port voltage of the lossless part of the power transmission line according to the geometric relation between the voltage and the current phasor at the protective installation position, and then calculating the measurement reactance of the lossless part of the power transmission line; and determining the protection range of the distance protection of the hybrid line according to the actual distance protection range.

Description

Hybrid line distance protection method based on lossless line equation
Technical Field
The invention relates to a distance protection method for a hybrid line based on a lossless line equation.
Background
Common hybrid lines include a cable-overhead hybrid line and a GIL-overhead hybrid line, electrical parameters of the cable/GIL are different from those of the overhead line, and accuracy of distance protection is related to line parameters, so that non-uniformity of parameters along the hybrid line may cause regional change of distance protection action, and in severe cases, distance protection misoperation may be caused. Therefore, the research on the distance protection suitable for the mixed line has important practical significance for guaranteeing the safe operation of the line.
According to the traditional overhead line distance protection, a line is equivalent to a centralized resistor and an inductor, the line impedance is in direct proportion to the line length, and the position of a fault is judged according to the measured impedance, so that the line protection principle with a certain protection length range is realized. The distance protection principle does not consider the distributed capacitance of the extra-high voltage line and the parameter change of the cable/GIL section, and the direct application of the distance protection principle to the hybrid line can cause serious results. Therefore, how to research the distance protection method of the hybrid line, which can accurately and reliably act, according to the electrical parameters of the hybrid line has important practical value.
Disclosure of Invention
In order to solve the problems, the invention provides a distance protection method for a hybrid line based on a lossless line equation, which is characterized in that a reactance measurement calculation formula under various fault conditions is given based on a lossless line transmission equation of an ultra-high voltage transmission line, the measured reactance is analyzed to form positive correlation with a tangent value of a fault position, and a setting value calculation method for distance protection of various sections of the hybrid line is given according to electrical parameters of various sections of the hybrid line and in combination with the protection ranges of a distance I section and a distance II section. The technical scheme is as follows:
a mixed line distance protection method based on a lossless line equation executes the following steps:
(1) based on the frequency domain parameters of the power transmission line, according to the transmission equation of the lossless line part of the power transmission line, deducing a measured reactance expression of the lossless line part when different types of faults occur to the line:
1) when an interphase fault occurs:
wherein XmabIs the measured reactance of the lossless section of line,respectively line voltage and line current at the protective installation, L1、C1Respectively a single-bit length positive sequence inductor and a positive sequence capacitor of the transmission line, omega is angular frequency, lmfIs the distance from the protective installation to the point of failure;
2) when single-phase earth fault occurs:
wherein XmaIs the measured reactance of the lossless section of line,respectively the a-phase voltage and the current at the protective installation,respectively, a-phase zero-sequence voltage and zero-sequence current, K, at the protective installation siteu、KiRespectively, zero sequence voltage and current compensation coefficients, the expressions are as followsThe following:
wherein L is0、C0The zero sequence inductance and the zero sequence capacitance are respectively the single-bit length zero sequence inductance and the zero sequence capacitance of the transmission line.
(2) According to the pure reactance characteristic presented by the transmission line lossless part, making a phasor diagram of voltage and current at the protection installation position, solving the port voltage of the lossless part according to the geometric relation between the voltage and the current phasor at the protection installation position, and then calculating the measurement reactance of the transmission line lossless part:
whereinIs the port voltage of the lossless section of line,is to protect the voltage of the installation site, phimTo protect the phase difference between the voltage and the current at the installation,is the phase of the voltage at the protection installation;
(3) determining the protection range of the hybrid line distance protection according to the actual distance protection range requirement, wherein the protection range comprises three conditions:
1) only contain overhead lines: only considering the parameters of the overhead line during the adjustment, and adjusting the parameters according to the relation of the measured reactance expression and the distance:
wherein XsetIIs the setting value of distance protection,/is the total length of the series-parallel line, LOV1Is a unit length positive sequence inductance, C, of an overhead lineOV1Is a unit length positive sequence capacitor of the overhead line;
2) contains a portion of the cable/GIL: and during setting, parameters of the GIL are considered, the reactance of the GIL is calculated, then the GIL is replaced by an overhead line with a certain length, the reactance values of the GIL and the overhead line are ensured to be equal, and finally, the overhead line parameters are used for setting:
wherein lmiIs the overhead line segment length l'OVIs the length of the equivalent overhead line used to replace the GIL;
3) including all cables/GIL, similar to case 2) tuning method:
wherein liiIs the length of the GIL segment.
The invention has the technical key points and beneficial effects that:
1. the method considers the distributed capacitance of the ultra-high voltage transmission line, has higher distance protection accuracy compared with the conventional centralized parameter, and can be used for the ultra-high voltage transmission line.
2. The method only needs to calculate the measured reactance at the protection installation position when in fault, does not need complex operation, reduces the operation amount and improves the operation speed.
3. The method considers the overhead line and cable/GIL section line parameters to set distance protection, and the protection range is accurate when the method is used for an ultra-high voltage cable/GIL-overhead mixed line; when the setting is carried out according to the parameters of the overhead line, the distance protection method is also suitable for the conventional uniform overhead line, and the setting method is simple, practical and easy to realize.
Description of the drawings:
fig. 1 is a schematic diagram of a lossless part of a power transmission line.
Fig. 2 is a schematic diagram of the power transmission line resistance concentration equivalent.
Fig. 3 is a graph of voltage and current phasors at m points at the location of the protection installation.
Fig. 4 is a schematic diagram of the distance protection range of the hybrid line.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Step A: and deducing a measurement reactance calculation formula of the lossless line part during the phase-to-phase fault and the ground fault according to a transmission equation of the lossless line of the power transmission line.
When the transmission line has a fault, the resistance of the line between the protection installation position and the fault point is ignored, and only the inductance and the capacitance exist in the line, so that the line between the protection installation position and the fault point can be equivalent to a lossless line, and the schematic diagram is shown in fig. 1. Wherein the content of the first and second substances,respectively protecting the voltage and the current at the installation position;the voltage at the fault point and the current flowing to the fault point f at the protection installation m are respectively. According to the line parameters, a frequency domain expression of the lossless line transmission equation is written in a column:
where L, C denotes the inductance and capacitance per unit length of the transmission line, ω 2 π f denotes the angular frequency, and l denotes the frequency of the transmission linemfTo protect the distance between the installation site and the point of failure. The method for deriving the measured reactance calculation formula under different faults according to the formula (1) comprises the following steps:
step 1: reactance calculation formula for phase-to-phase fault measurement
When the phase-to-phase fault occurs, taking A, B phases as an example, the line voltage at the protection installation is calculated according to the formula (1)Sum line current
In the formulae (2) and (3), L1And C1Respectively the positive sequence inductance and the capacitance of the transmission line,in order to be the line voltage at the fault point,to protect the fault line current flowing from installation m to fault point f. The voltage at the fault point being 0, i.e.Carrying in formula (2) and formula (3), and then simplifying according to Euler's formula:
the measured reactance of the line is calculated according to equation (4) as:
step 2: reactance calculation formula for single-phase earth fault measurement
When single-phase earth fault occurs, the fault phase is decomposed into positive sequence, negative sequence and zero sequence networks by using a symmetrical component method, and the voltage of the protection installation position is calculated according to the formula (1)And current
In the formulae (6) and (7), L1And C1、L2And C2、L0And C0Positive sequence, negative sequence, zero sequence inductance and capacitance of the transmission line respectively, and the voltage at the fault point is 0, namelyCarry over formula (6) and formula (7), then reduce to according to euler's formula:
wherein the content of the first and second substances,the detailed expression is as follows:
and because:
after the term-shifting transformation of the formula (13),andhas the following relationship:
wherein, Ku、KiThe zero sequence voltage and current compensation coefficients are respectively represented by the following specific expressions:
from equations (8) and (14) we can obtain:
the measured reactance of the line is calculated according to equation (16) as:
and B: and calculating the measured impedance of the lossless line part of the power transmission line according to the known electrical quantity measured at the protective installation.
Neglecting the error caused by the line resistance, the distributed resistance in the line is equivalent to a concentration parameter and is placed at one end of the line to simulate the amplitude attenuation of the voltage and current traveling wave caused by the line resistance, and the schematic diagram is shown in fig. 2. Wherein R.lmfTo protect the lumped resistance between the installation site and the fault point;is the voltage attenuated by the lumped resistance.
According to the equations (5) and (17), the lossless sections can be equivalent to pure reactance in the inter-phase fault and the ground fault, so thatAndthe phases differ by 90. The voltage drop on the lossless line in fig. 2 is therefore 90 out of phase with the voltage drop on the lumped resistance. A phasor diagram is made from its magnitude and phase as shown in figure 3. Wherein the content of the first and second substances,is the phase angle difference between the voltage and current phasors at the m-point, is a known quantity,is the voltage on the lumped resistor, which is in conjunction with the currentIn the same phase, the phase of the signal is changed,andthe phase difference is 90 DEG and the magnitude isIn thatThe projection in the phasor direction can be obtained from the geometric relation shown in the phasor diagram
The measured reactance in each fault case can then be found from equations (5) and (17).
And C: and setting the distance I section and the distance II section according to the line section where the distance protection range tail end is located and the line parameters of the overhead line and the cable/GIL.
It can be seen from equations (5) and (17) that the measured reactance of the equivalent lossless part of the extra-high voltage transmission line and the fault distance are in a tangent function relationship, and therefore, the setting value of the reactance in the distance protection setting is set according to the tangent function of the distance.
Fig. 4 is a schematic diagram of the distance protection range. Wherein lmiIs the length of 1 segment of overhead line, lijIs the cable/GIL section length, lnjIs the length of the overhead line 2. The protection range of the distance I section is 85% of the total length of the line, the distance I section possibly comprises a cable/GIL section, and the distance I section needs to be adjusted according to conditions due to the difference of electrical parameters between the cable/GIL and the overhead line. A setting method is introduced by taking a GIL-overhead mixed line as an example:
(1) if the distance I section protection range does not include the GIL section, the line parameters of the GIL section are not considered during setting, and the setting value of the distance I section reactance is as follows:
XsetI＝jZC-OV1tan(ωTOV1·0.85l) (19)
in the formula (19), l is the total length of the parallel-serial line;the capacitance can be obtained by the unit length positive sequence inductance and the unit length positive sequence capacitance of the overhead line.
(2) If the distance segment I protection range includes a portion of the GIL segment, the reactance of the GIL contained within the protection range is first calculated:
XGIL＝jZC-GIL1tan(ωTGIL1·lGIL) (20)
in the formula (20) < CHEM >GIL＝(0.85l-lmi) Is the length of the GIL contained within the scope of protection; positive sequence per unit length by GILAnd (4) obtaining the inductance and the unit length positive sequence capacitance.
Then with a length of l'OVHas an alternative length of lGILThe GIL of (a) ensures that the reactance of the two is consistent, namely:
jZC-GIL1tan(ωTGIL1·lGIL)＝jZC-OV1tan(ωTOV1·l′OV) (21)
from the formula (21), the length l 'of the equivalent overhead line can be obtained'OVComprises the following steps:
calculating a reactance setting value at a distance I section:
XsetI＝jZC-OV1tan(ωTOV1·(lmi+l′OV)) (23)
(3) if the distance I section protection range comprises the whole length of the GIL section, the distance I section protection range is approximately adjusted according to the adjusting method of the condition (2), and the reactance adjusting value of the distance I section at the moment is as follows:
XsetI＝jZC-OV1tan(ωTOV1·(0.85l-lij+l′OV)) (24)
since the distance II section cooperates with the distance I section of the next section of line to protect the entire length of the line of this section, it includes the entire length of the GIL section, i.e., the setting manner is similar to the above case (3). The method for setting the distance protection of each section of the cable-overhead mixed line is similar to the method.

Claims (1)

1. A mixed line distance protection method based on a lossless line equation executes the following steps:
(1) based on the frequency domain parameters of the power transmission line, according to the transmission equation of the lossless line part of the power transmission line, deducing a measured reactance expression of the lossless line part when different types of faults occur to the line:
1) when an interphase fault occurs:
wherein XmabIs the measured reactance of the lossless section of line,respectively line voltage and line current at the protective installation, L1、C1Respectively a single-bit length positive sequence inductor and a positive sequence capacitor of the transmission line, omega is angular frequency, lmfIs the distance from the protective installation to the point of failure;
2) when single-phase earth fault occurs:
wherein XmaIs the measured reactance of the lossless section of line,respectively the a-phase voltage and the current at the protective installation,respectively, a-phase zero-sequence voltage and zero-sequence current, K, at the protective installation siteu、KiZero sequence voltage and current compensation coefficients are respectively represented as follows:
wherein L is0、C0The zero sequence inductance and the zero sequence capacitance are respectively the single-bit length zero sequence inductance and the zero sequence capacitance of the transmission line;
(2) according to the pure reactance characteristic presented by the transmission line lossless part, making a phasor diagram of voltage and current at the protection installation position, solving the port voltage of the lossless part according to the geometric relation between the voltage and the current phasor at the protection installation position, and then calculating the measurement reactance of the transmission line lossless part:
whereinIs the port voltage of the lossless section of line,is to protect the voltage of the installation site, phimTo protect the phase difference between the voltage and the current at the installation,is the phase of the voltage at the protection installation;
(3) determining the protection range of the hybrid line distance protection according to the actual distance protection range requirement, wherein the protection range comprises three conditions:
1) only contain overhead lines: only considering the parameters of the overhead line during the adjustment, and adjusting the parameters according to the relation of the measured reactance expression and the distance:
wherein XsetIIs a setting value of distance protection, L is the total length of the series-parallel line, LOV1Is a unit length positive sequence inductance, C, of an overhead lineOV1Is a unit length positive sequence capacitor of the overhead line;
2) contains a portion of the cable/GIL: and (2) calculating the reactance of the cable/GIL by considering the parameters of the cable/GIL at regular time, then replacing the cable/GIL with an overhead line with a certain length to ensure that the reactance values of the cable/GIL and the overhead line are equal, and finally setting by using the parameters of the overhead line:
wherein lmiIs segment length l 'of overhead line 1'OVIs the length of the equivalent overhead line used to replace the cable/GIL;
3) including all cables/GIL, similar to case 2) tuning method:
wherein lijIs the length of the cable/GIL section.
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CN100570791C (en) * 2007-06-06 2009-12-16 清华大学 A kind of single phase ground fault relay protecting method based on the negative sequence reactance relay
CN100576682C (en) * 2008-03-07 2009-12-30 西安交通大学 Band serial compensation capacitance transmission line distance protecting method based on Model Identification
CN102361320A (en) * 2011-10-26 2012-02-22 国电南京自动化股份有限公司 Method for protecting break variable distance based on time domain model
CN103354354B (en) * 2013-06-26 2016-03-02 国家电网公司 Be applicable to impedance protecting method and the device of micro-capacitance sensor
CN107979074B (en) * 2017-11-15 2019-04-02 湖北省电力勘测设计院有限公司 Adapt to the Sudden Changing Rate distance protection setting method of fault current limiter

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