CN108226713B - Concentric relaxation depression domain analysis method for voltage sag - Google Patents

Concentric relaxation depression domain analysis method for voltage sag Download PDF

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CN108226713B
CN108226713B CN201810112522.9A CN201810112522A CN108226713B CN 108226713 B CN108226713 B CN 108226713B CN 201810112522 A CN201810112522 A CN 201810112522A CN 108226713 B CN108226713 B CN 108226713B
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田立军
刘冲
张天豪
侯燕文
高运兴
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Shandong 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
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Abstract

The invention discloses a voltage sag concentric relaxation sag domain analysis method, which comprises the following steps: solving positive sequence, negative sequence and zero sequence node impedance matrixes of the power grid; determining the fault type and fault point causing the voltage sag; forming a node impedance matrix after a fault occurs; obtaining a voltage sag value of a power grid; a failed concentric relaxed depressed region is determined. The invention has the beneficial effects that: the concentric relaxation depression domain analysis with the fault point as the center can effectively reduce the workload of depression domain analysis, can more conveniently judge the voltage sag influence range caused by the short-circuit fault, provides a judgment basis for the indemnity liability attribution problem of economic loss of power supply enterprises and power users due to the voltage sag, and has good practical application value.

Description

Concentric relaxation depression domain analysis method for voltage sag
Technical Field
The invention relates to a concentric relaxation dip domain analysis method for voltage sag.
Background
With the rapid development of modern industry, a great deal of sensitive loads such as a microprocessor-based control system, load equipment including power electronic devices, and computers and programmable controllers are put into a power grid, and in a case of complaints about power quality, user complaints caused by voltage sag account for more than 80%, and voltage sag has become the most important power quality problem. The voltage sag will cause the production stop of the factory and the stop of the sensitive load and even damage, and huge economic loss is brought. The analysis of the voltage sag and the sag domain thereof has important theoretical and practical significance.
At present, the conventional analysis of the sag domain is essentially to determine the area of a fault point where a sensitive load cannot normally work by calculating the voltage sag condition of the sensitive load when a power system is in a short-circuit fault, and the following problems mainly exist:
1. sensitive loads in the power grid are increased, and traditional sunken area analysis is carried out on each sensitive load, so that workload of sunken area analysis is greatly increased.
2. The definition of respective responsibility and effective compensation of the power supply and the power utilization in the voltage sag accident is not facilitated.
Disclosure of Invention
The invention aims to provide a concentric relaxation sag domain analysis method for voltage sag, which is used for conveniently and concisely analyzing the voltage sag of a power grid and making the responsibility division of economic loss caused by the voltage sag be clear, and determines that a voltage sag concentric relaxation sag domain is an area with the voltage sag amplitude lower than a certain voltage threshold value caused by a fault with a fault point as the center; when the sensitive load is in the concentric relaxation concave area, the voltage sag caused by the fault indicates that the sensitive load cannot work normally, and power supply enterprises need to compensate power consumers according to related laws and signed power supply contracts; when the sensitive load is outside the concentric relaxation concave area, the voltage sag caused by the fault does not influence the normal work of the sensitive load, and the power supply enterprise does not need to fulfill the economic compensation obligation of the sensitive load.
In order to achieve the purpose, the invention adopts the following technical scheme that:
a concentric relaxation dip domain analysis method of voltage sag, comprising the steps of:
(1) respectively obtaining positive sequence, negative sequence and zero sequence node impedance matrixes of the power grid according to actual power grid parameters and structures;
(2) determining the type of the power grid fault causing the voltage sag according to the voltage amplitude information and the voltage zero sequence component information; determining a fault point causing voltage sag through fault location;
(3) forming a node impedance matrix after the fault occurs according to the mutual impedance and the self impedance of the fault point;
(4) dividing the faults of the power grid into symmetrical faults and asymmetrical faults; respectively solving the voltage sag values of the power grid under the two fault types;
(5) and determining the concentric relaxation depression domain of the fault according to the obtained power grid voltage sag value.
Further, in the step (2), the types of the grid faults causing the voltage sag to occur are specifically:
the types of faults include: single-phase ground faults, two-phase short-circuit ground faults, two-end short-circuit faults and three-phase short-circuit faults;
for one phase voltage amplitude value lower than the average value, the other two phases higher than the average value are determined to be single-phase earth faults;
for the two-phase voltage amplitude value lower than the average value, the other phase higher than the average value is determined as two-phase short circuit grounding fault or two-end short circuit fault;
and determining that the three-phase voltage amplitude is temporarily reduced to similar amplitude as a three-phase fault.
Further, in the step (2), the fault location where the fault point causing the voltage sag occurs includes: bus bar nodes or grid lines.
Further, in the step (3), forming a node impedance matrix after the fault occurs specifically includes:
if the fault occurs on the line, taking the fault point as a newly added bus node of the power grid, and adding a corresponding node impedance matrix by one step;
adopting the fault position parameter to represent the fault occurrence position on the transmission line, and obtaining a functional relation between the mutual impedance and the self impedance of the relevant fault point in the node impedance matrix and the fault parameter;
and finishing the node impedance matrix after the fault according to the mutual impedance and the self-impedance of the fault point.
Further, the fault location parameter λ is specifically:
Figure BDA0001569680680000021
in the formula IjfRepresents the distance between the first node j of the fault line and the fault point f, ljkIndicating the total length of the faulty line j-k.
Further, the mutual impedance Z of the fault point fmfAnd self-impedance ZffThe functional relation with the fault parameter lambda is specifically as follows:
Figure BDA0001569680680000022
Figure BDA0001569680680000031
wherein, n is 1,2,0 respectively represents positive sequence, negative sequence and zero sequence components when asymmetric fault occurs;
Figure BDA0001569680680000032
is the transimpedance between fault point f and node m,
Figure BDA0001569680680000033
is the transimpedance of node m and fault line head node j,
Figure BDA0001569680680000034
the transimpedance of node m and fault line end node k,
Figure BDA0001569680680000035
the self-impedance of the fault line head node j,
Figure BDA0001569680680000036
the transimpedance of the faulty line head node j and the faulty line end node k,
Figure BDA0001569680680000037
the self-impedance of the faulty line end node k.
Further, in the step (4), for a symmetric fault:
Figure BDA0001569680680000038
wherein, UmWhen a three-phase short-circuit fault occurs at a fault point f, the voltage sag amplitude value at any node m is shown; zmfRepresenting the mutual impedance between node m and fault point f, ZffIs the positive sequence self-impedance of the fault point f,
Figure BDA0001569680680000039
is the effective value of the voltage of the node m before the fault occurs,
Figure BDA00015696806800000310
the effective value of the voltage of the fault point f before the fault occurs.
Further, in the step (4), for an asymmetric fault:
if voltage sag occurs at any node m, the voltage sag amplitude U issagIs composed of
Usag＝min{Um,A,Um,B,Um,C}；
Wherein, Um,A、Um,B、Um,CRespectively is an ABC three-phase voltage effective value at any node m.
Further, in the step (5), the faulty concentric relaxation pit area is determined, specifically:
traversing each branch in the power network, calculating the voltage dip per unit value of the head and tail nodes of each branch, and comparing the voltage dip per unit value with a voltage threshold value:
when the voltage per unit value of the node is smaller than the threshold value, the node falls into the concentric relaxation concave area;
when the voltage per unit value of the node is larger than the threshold value, the node is outside the concentric relaxation concave domain;
when the voltage dip per unit value of the node or the line is equal to the voltage threshold, the voltage dip per unit value is a critical dip point, namely the boundary of the concentric relaxation concave domain;
and obtaining the concentric relaxation depression domain of the power grid by traversing all branches of the power grid.
The invention has the beneficial effects that:
the concentric relaxation depression domain analysis with the fault point as the center can effectively reduce the workload of depression domain analysis, can more conveniently judge the voltage sag influence range caused by the short-circuit fault, provides a judgment basis for the indemnity liability attribution problem of economic loss of power supply enterprises and power users due to the voltage sag, and has good practical application value.
Drawings
FIG. 1 is a schematic flow chart of a concentric relaxation dip domain analysis method of voltage sag;
FIG. 2 is a graph showing the results of concentric relaxation dip domain analysis of voltage sag.
The specific implementation mode is as follows:
the invention will be further explained with reference to the drawings.
The invention discloses a voltage sag concentric relaxation sag domain analysis method, which comprises the following steps as shown in figure 1:
(1) solving positive sequence, negative sequence and zero sequence node impedance matrixes of the power grid;
the positive sequence and the negative sequence are specifically as follows:
and obtaining the actual power grid parameters and structures. And (4) considering that the positive sequence node impedance matrix and the negative sequence node impedance matrix are completely the same, and solving one of the positive sequence node impedance matrix and the negative sequence node impedance matrix.
The zero-sequence node impedance is specifically as follows:
a zero-sequence node impedance matrix is formed by analyzing a zero-sequence network structure, and when the wiring mode of the transformer is YNy, Yyn, Yy and Dd types (the capital is the primary side and the small is the secondary side), wherein Y represents star connection, D represents triangular connection, and N represents that a neutral line is not grounded. Namely, the zero sequence component of the temporarily reduced voltage can not pass through the transformer, the zero sequence component is subtracted from the temporarily reduced voltage after the transformation of the transformer when the voltage is not transformed, and the zero sequence impedance can be set to be infinite. The zero sequence impedance of other lines can be obtained by actual measurement or by calculation to obtain an approximate value, which is greatly different from the impedance matrix of the positive sequence and negative sequence nodes.
(2) Determining the fault type and fault point causing the voltage sag;
judging and determining that the fault belongs to a single-phase earth fault, a two-phase short circuit earth fault, a two-end short circuit fault and a three-phase short circuit fault:
for single-phase earth faults, the amplitude of one phase voltage is lower than the mean value, and the amplitudes of the other two phases are higher than the mean value;
for two-phase short-circuit ground faults and two-end short-circuit faults, the amplitude values of two phases of voltages are lower than the average value, the amplitude value of the other phase of voltages is higher than the average value, and the two-phase short-circuit ground fault is determined by the larger voltage zero-sequence component;
and for the three-phase fault, the three-phase voltage amplitude values are all subjected to temporary drop with similar amplitude.
The wide application of intelligent instruments, intelligent monitoring equipment and advanced communication technology in power systems makes the above voltage information for judgment easily available.
The fault position of the fault causing the voltage sag can be a bus node or a position on a line. And the specific fault position accurately positions the fault through an equipment terminal FTU, a DTU and the like.
(3) Forming a node impedance matrix after a fault occurs;
if the fault occurs on the line, the fault point f can be used as a newly added bus node of the power grid, and the corresponding node impedance matrix is added by one step. To indicate the location of the fault on the transmission line, a fault location parameter λ is used as follows:
Figure BDA0001569680680000051
in the formula IjfIndicating the distance, l, from the line head node to the fault point fjkThe total length of the branch j-k is represented, and the fault occurrence position is represented by a fault parameter lambda, so that the mutual impedance Z of a fault point f in the node impedance matrix can be obtainedmfAnd self-impedance ZffAs a function of the fault parameter λ, as shown in the following equation:
Figure BDA0001569680680000052
Figure BDA0001569680680000053
n-1, 2,0 denotes the positive, negative and zero sequence components when an asymmetric fault occurs.
Figure BDA0001569680680000054
Is the transimpedance between fault point f and node m,
Figure BDA0001569680680000055
is the transimpedance of node m and fault line head node j,
Figure BDA0001569680680000056
the transimpedance of node m and fault line end node k,
Figure BDA0001569680680000057
the self-impedance of the fault line head node j,
Figure BDA0001569680680000058
the transimpedance of the faulty line head node j and the faulty line end node k,
Figure BDA0001569680680000059
the self-impedance of the faulty line end node k.
And finishing the node impedance matrix after the fault according to the mutual impedance and the self impedance of the fault point.
Short-circuit fault may occur at the bus, and if the fault occurs on the bus, the original impedance matrix is used, and nodes are not required to be added.
(4) Obtaining a voltage sag value of a power grid;
when short-circuit faults occur, the voltage value of each bus node is obtained, voltage sag analysis is carried out on the power grid by adopting a voltage sag analytical method, and the faults occurring in the power grid are divided into two categories, namely symmetric faults and asymmetric faults. 1) Symmetrical fault
According to the superposition principle, the voltage sag value of the system with the fault can be obtained by superposing the normal component and the fault component of the voltage.
The off-diagonal element Z is defined by the node impedance matrixjiRepresents the transimpedance, as shown in the following equation:
Figure BDA00015696806800000510
its value represents the voltage U at the j node when the i node injects unit current and the rest nodes do not inject currentjUnit current I at node IiThe ratio of (a) to (b).
The fault component DeltaU of the node m can be obtained by the definition of the mutual impedancemfThe following formula:
ΔUmf＝IfZmf
in the formula IfIndicating fault current, ZmfRepresenting the mutual impedance between node m and fault point f.
Diagonal element Z of the nodal impedance matrixiiRepresents the self-impedance, as shown in the following equation:
Figure BDA0001569680680000061
its value represents the voltage U at the i-node when the i-node injects unit current and the rest nodes do not inject currentiAnd the current I at the I nodeiThe ratio of (a) to (b). From the above definition of the self-impedance I can be obtainedfAs shown in the following formula:
Figure BDA0001569680680000062
zfis the fault resistance at node f. Metallic short-circuit fault zfWhen 0, the formula:
Figure BDA0001569680680000063
Umand when the three-phase short-circuit fault occurs at the fault point f, the effective value of the voltage at any node m is the voltage sag amplitude. ZffIs the positive sequence self-impedance of the fault point f,
Figure BDA0001569680680000064
is the effective value of the voltage of the node m before the fault occurs,
Figure BDA0001569680680000065
the effective value of the voltage of the fault point f before the fault occurs.
2) Asymmetric fault
Under the condition that the power grid has asymmetric faults, the system equivalent network can be divided into a positive sequence network, a negative sequence network and a zero sequence network by adopting a symmetric component method, and each sequence network is calculated by adopting a superposition principle. The following analysis is based on phase A.
The effective value of the three-phase voltage at any node m during single-phase earth fault is as follows:
Figure BDA0001569680680000066
wherein α ej120°。
The effective value of the three-phase voltage at any node m during the BC interphase short circuit fault is as follows:
Figure BDA0001569680680000071
when the BC is in ground fault, the effective value of the three-phase voltage at any node m is as follows:
Figure BDA0001569680680000072
according to the definition of the voltage sag amplitude: the voltage sag amplitude is the magnitude of the voltage root mean square value in the voltage sag period, and the three-phase lowest phase voltage is taken as the voltage sag amplitude of the node. Therefore, if voltage sag occurs at any node m, the voltage sag amplitude U is obtainedsagIs composed of
Usag＝min{Um,A,Um,B,Um,C}。
(5) A failed concentric relaxed depressed region is determined.
Traversing each branch in the power network, calculating the voltage sag per unit value of the head node and the tail node of each branch, comparing the voltage sag per unit value with a voltage threshold, when the voltage per unit value of a node is less than the threshold, the node falls into a concentric relaxation concave domain, when the voltage per unit value of the node is more than the threshold, the node is out of the concentric relaxation concave domain, and when the voltage sag per unit value of the node or a line is equal to the voltage threshold, the node or the line is a critical sag point, namely the boundary of the concentric relaxation concave domain. By traversing all branches of the power grid, a concentric sag domain of the power grid is obtained, and a concentric sag domain range map is made, as shown in fig. 2.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims (7)

1. A concentric relaxation dip domain analysis method of voltage sag, comprising the steps of:
(1) respectively obtaining positive sequence, negative sequence and zero sequence node impedance matrixes of the power grid according to actual power grid parameters and structures;
(2) determining the type of the power grid fault causing the voltage sag according to the voltage amplitude information and the voltage zero sequence component information; determining a fault point causing voltage sag through fault location;
in the step (2), the type of the power grid fault causing the voltage sag is specifically:
the types of faults include: single-phase ground faults, two-phase short-circuit ground faults, two-end short-circuit faults and three-phase short-circuit faults;
for one phase voltage amplitude value lower than the average value, the other two phases higher than the average value are determined to be single-phase earth faults;
for the two-phase voltage amplitude value lower than the average value, the other phase higher than the average value is determined as two-phase short circuit grounding fault or two-end short circuit fault;
determining that three-phase faults occur when the three-phase voltage amplitude values are all subjected to temporary drop with similar amplitude;
(3) forming a node impedance matrix after the fault occurs according to the mutual impedance and the self impedance of the fault point;
in the step (3), the forming of the node impedance matrix after the fault occurs specifically includes:
if the fault occurs on the line, taking the fault point as a newly added bus node of the power grid, and adding a corresponding node impedance matrix by one step;
adopting the fault position parameter to represent the fault occurrence position on the transmission line, and obtaining a functional relation between the mutual impedance and the self impedance of the relevant fault point in the node impedance matrix and the fault parameter;
completing a node impedance matrix after the fault according to the mutual impedance and the self-impedance of the fault point;
(4) dividing the faults of the power grid into symmetrical faults and asymmetrical faults; respectively solving the voltage sag values of the power grid under the two fault types;
(5) and determining the concentric relaxation depression domain of the fault according to the obtained power grid voltage sag value.
2. The method for analyzing concentric sag domain of voltage sag as claimed in claim 1, wherein the step (2) of determining the fault location of the fault point causing the voltage sag comprises: bus bar nodes or grid lines.
3. The method of claim 1, wherein the fault location parameter λ is specifically:
Figure FDA0002375452200000011
in the formula IjfRepresents the distance between the first node j of the fault line and the fault point f, ljkIndicating the total length of the faulty line j-k.
4. The method of claim 1, wherein the transimpedance of fault f, the transimpedance of the Z, ismfAnd self-impedance ZffThe functional relation with the fault parameter lambda is specifically as follows:
Figure FDA0002375452200000021
Figure FDA0002375452200000022
where n is 1,2, and 0 each represents positive when an asymmetric fault occursSequence, negative sequence and zero sequence components;
Figure FDA0002375452200000023
is the transimpedance between fault point f and node m,
Figure FDA0002375452200000024
is the transimpedance of node m and fault line head node j,
Figure FDA0002375452200000025
the transimpedance of node m and fault line end node k,
Figure FDA0002375452200000026
the self-impedance of the fault line head node j,
Figure FDA0002375452200000027
the transimpedance of the faulty line head node j and the faulty line end node k,
Figure FDA0002375452200000028
the self-impedance of the faulty line end node k.
5. The concentric sag domain analysis method for voltage sag according to claim 1, wherein in step (4), for a symmetric fault:
Figure FDA0002375452200000029
wherein, UmWhen a three-phase short-circuit fault occurs at a fault point f, the voltage sag amplitude value at any node m is shown; zmfRepresenting the mutual impedance between node m and fault point f, ZffIs the positive sequence self-impedance of the fault point f,
Figure FDA00023754522000000210
is the effective value of the voltage of the node m before the fault occurs,
Figure FDA00023754522000000211
the effective value of the voltage of the fault point f before the fault occurs.
6. The concentric sag domain analysis method for voltage sag according to claim 1, wherein in the step (4), for an asymmetric fault:
if voltage sag occurs at any node m, the voltage sag amplitude U issagIs composed of
Usag＝min{Um,A,Um,B,Um,C}；
Wherein, Um,A、Um,B、Um,CRespectively is an ABC three-phase voltage effective value at any node m.
7. The method for analyzing concentric sag depression domains of voltage sag according to claim 1, wherein in the step (5), the concentric sag depression domain with the fault is determined, and specifically:
traversing each branch in the power network, calculating the voltage dip per unit value of the head and tail nodes of each branch, and comparing the voltage dip per unit value with a voltage threshold value:
when the voltage per unit value of the node is smaller than the threshold value, the node falls into the concentric relaxation concave area;
when the voltage per unit value of the node is larger than the threshold value, the node is outside the concentric relaxation concave domain;
when the voltage dip per unit value of the node or the line is equal to the voltage threshold, the voltage dip per unit value is a critical dip point, namely the boundary of the concentric relaxation concave domain;
and obtaining the concentric relaxation depression domain of the power grid by traversing all branches of the power grid.
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