CN103823998B - Weak cross section determination method taking influence of network topology changes on power transmission capacity into consideration - Google Patents

Abstract

The invention provides a weak cross section determination method taking influence of network topology changes on the power transmission capacity into consideration. The weak cross section determination method comprises the following steps of calculating the static stable power transmission capacity of power transmission cross sections in which the network topology changes are taken into consideration, calculating the load rate of the power transmission cross sections, carrying out screening on the power transmission cross sections according to the degree of influence of the network topology changes on the power transmission capacity, and determining the weak cross section. According to the weak cross section determination method taking influence of the network topology changes on the power transmission capacity into consideration, evaluation is carried out on the normal operation state of the given cross sections and the state, generated after the network topology changes happen, of the given cross sections, the stability margin and the power transmission capacity in the normal state are evaluated according to the static power transmission capacity, the degree of influence on the system power transmission capacity and the system margin after the network topology changes happen is evaluated in a power transmission cross section line N-1 disconnection mode and multi-circuit line N-M disconnection mode, the degree of weakness of the cross sections is comprehensively evaluated, and the weak cross section is recognized.

Description

Weak section determination method considering influence of network topology change on power transmission capacity

Technical Field

The invention relates to a determination method, in particular to a weak section determination method considering the influence of network topology change on power transmission capacity.

Background

In the offline calculation and analysis of the power system, the concerned section is basically determined, but the weak degree of the section changes along with the change of the actual situation, and the analysis and the judgment are required to be continuously carried out, so that abundant experience is accumulated in the offline calculation and analysis.

And determining a weak power transmission section, wherein a large number of calculation methods are usually adopted in the practical application process, for example, a large number of transient stability calculations are carried out, and a section which is easy to destabilize, an oscillation center section and the like are searched. For the concerned section, usually, electromechanical transient simulation software is needed to calculate the transmission limit, considering the transient, dynamic stability and overload of the system, the transmission capacity of the section is calculated, and if the margin relative to the current actual power is smaller, the section is a more critical section. The static stability limit is also one of important methods for evaluating the transmission capacity of the section, and the static stability limit in an actual system is usually higher, so that a method for calculating the static stability limit is not usually adopted, and the static stability limit is calculated only on a weak long-distance transmission line or a weak tie line. However, the static stability limit has a close relationship with the transient stability limit and the system stability level, and is still one of the important methods for evaluating the section weakness.

There is no good method for judging the weak degree of the section in the online system, and offline calculation analysis experience can be used for reference, but the online system has high requirement on time, so that the online system cannot depend on a large amount of calculation, and research is needed.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a weak section determining method considering the influence of network topology change on the power transmission capacity, which is characterized in that the given section is evaluated respectively according to a normal operation state and a state after the network topology change, the stability margin and the power transmission capacity in the normal state are evaluated by adopting the static power transmission capacity, the influence degree on the power transmission capacity and the margin of a system after the network structure change is evaluated by adopting a mode of disconnecting a power transmission section line N-1 and disconnecting a multi-circuit line N-M, and finally, the weak section is comprehensively evaluated and the weak section is identified.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

the invention provides a weak section determination method considering the influence of network topology change on power transmission capacity, which comprises the following steps:

step 1: calculating the static stable power transmission capacity of a power transmission section considering the network topology change;

step 2: calculating the load rate of the power transmission section;

and step 3: and screening the power transmission sections according to the influence degree of the network topology change on the power transmission capacity, and determining the weak sections.

In the step 1, the power transmission section comprises a single-channel power transmission section and a multi-channel power transmission section; the static stable power transmission capacity of the single-channel power transmission section and the multi-channel power transmission section respectively uses P_maxAndand (4) showing.

Static stable power transmission capacity P of single-channel power transmission section_maxThe calculation process is as follows:

1) calculating the impedance matrix of nodes 1 and 2 on two sides of a single-channel power transmission section, comprising the following steps of:

wherein Z is_eqRepresenting the impedance matrix of nodes 1 and 2 on both sides of a single channel transmission section, Z₁₁、Z₂₂Self-impedance of node 1, node 2, respectively, Z₁₂And Z₂₁Are both the transimpedance of node 1 and node 2;

2) and calculating admittance matrixes corresponding to the nodes 1 and 2, wherein the admittance matrixes comprise:

wherein, Y_eqDenotes the admittance matrix, Y, corresponding to node 1 and node 2₁₁、Y₂₂Self-admittance, Y, of node 1, respectively node 2₁₂And Y₂₁Are both the transimpedance of node 1 and node 2;

3) calculating equivalent impedance of a single-channel power transmission section, comprising the following steps:

wherein, X_ΣEquivalent impedance of a single-channel power transmission section;

4) assuming that the voltages of the node 1 and the node 2 are both 1, the static stable power transmission capacity P of a single-channel power transmission section_maxCalculated according to the following formula:

wherein E is₁And E₂Representing the voltages at node 1 and node 2, respectively.

Aiming at a multi-channel power transmission section, the static stable power transmission capacity of the power transmission section in a normal state, an N-1 state and an N-M state is calculated according to the following processWherein N represents the total loop number of the multi-channel power transmission section, and M represents the loop number of one channel in the multi-channel power transmission section;

1) node numbers on two sides of all power transmission section channels are counted, and nodes with the same node numbers are adopted for combination;

2) calculating an impedance matrix of a multi-channel power transmission section, comprising the following steps:

wherein,impedance matrix, Z, representing a single channel transmission section₁₁、Z₂₂、...、Z_nnSelf-impedance of nodes 1, 2, …, n, respectively, Z₁₂、Z₂₁、...、Z_1n、Z_n1Is the mutual impedance between different nodes;

3) and calculating an admittance matrix corresponding to the node, wherein the admittance matrix comprises the following components:

wherein,representing admittance matrices, Y, to the node₁₁、Y₂₂、...、Y_nnSelf-admittance, Y, of nodes 1, 2, …, n, respectively₁₂、Y₂₁、...、Y_1n、Y_n1Is the mutual impedance between different nodes;

4) calculating equivalent impedance of multi-channel power transmission section

Adding a row and a column in the admittance matrix corresponding to the node, then carrying out elimination calculation on the admittance matrix corresponding to the node, and obtaining an addition row of diagonal elements after calculation, namely the equivalent admittance between the two nodesEquivalent impedance of multi-channel power transmission sectionExpressed as:

5) static stable power transmission capacity of multi-channel power transmission sectionExpressed as:

in step 2, when the load factor of the power transmission section is represented by η, the following are provided:

wherein, P_loadThe actual power of the transmission profile is represented.

In the step 3, the following three basic principles are adopted to screen the transmission sections, and the final weak section is determined in a step-by-step reduction standard mode according to a set load rate fixed value;

(1) in a normal state, a power transmission section with a higher load rate should be reserved;

(2) in the N-1 state, the load rate is changed greatly, and the load rate is higher after N-1, which is reserved;

(3) in the N-M state, the load rate changes more and the load rate after N-M should be higher.

Compared with the prior art, the invention has the beneficial effects that:

the method is simple and feasible, the adopted method is the extension of the basic theoretical method in a complex power system, and the method is simple and feasible.

The method can rapidly screen a large number of sections, and can consider calculation and check of a large number of derivative sections formed after the circuit is disconnected, so that the consideration is comprehensive;

the method adopts an approximately rapid calculation method, can greatly improve the calculation speed under the condition of ensuring certain precision, and ensures the practicability under the online condition.

Drawings

FIG. 1 is a schematic diagram of a simple two-machine system in an embodiment of the invention;

FIG. 2 is a schematic diagram of an equivalent network with nodes on two sides of a power transmission section calculated as ports according to an embodiment of the present invention;

fig. 3 is a schematic diagram of an equivalent network considering power supplies on two sides, where nodes on two sides of a power transmission section are calculated as ports in the embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

The invention provides a weak section determination method considering the influence of network topology change on power transmission capacity, which comprises the following steps:

step 1: calculating the static stable power transmission capacity of a power transmission section considering the network topology change;

step 2: calculating the load rate of the power transmission section;

and step 3: and screening the power transmission sections according to the influence degree of the network topology change on the power transmission capacity, and determining the weak sections.

For a simple two-machine system, as shown in fig. 1, assuming that the internal potentials of the generators on both sides can be kept constant, the maximum exchange power between the two is P_maxThe method comprises the following steps:

the formula has a strict theoretical basis and can reflect the power transmission capacity of a simple system to a certain extent. From this formula, it can be seen that the influence on the power transmission capacity of the system is mainly the equivalent reactance of the system, besides the generator potential, which is partly determined by the voltage control capacity of the generator, and the reactance is also reflected by the network structure of the system.

For a practical large-scale power system, it is impossible to achieve accurate estimation of the power transmission capability with such a simple calculation formula. However, the basic physical characteristics of the formula reaction can also be applied to simple analysis of an actual power system, and the size of the equivalent reactance can reflect the physical characteristics of an actual power grid to a certain extent. Aiming at the requirement of fast screening of a large number of actually searched sections, if the strength of the sections can be basically qualitatively and reasonably reflected to carry out fast screening, most sections which are not concerned are removed, and the rest sections are evaluated in detail, the method still has important value for the application of an actual system.

In the step 1, the power transmission section comprises a single-channel power transmission section and a multi-channel power transmission section; the static stable power transmission capacity of the single-channel power transmission section and the multi-channel power transmission section respectively uses P_maxAndand (4) showing.

Static stable power transmission capacity P of single-channel power transmission section_maxThe calculation process is as follows:

1) calculating the impedance matrix of nodes 1 and 2 on two sides of a single-channel power transmission section, comprising the following steps of:

wherein Z is_eqRepresenting the impedance matrix of nodes 1 and 2 on both sides of a single channel transmission section, Z₁₁、Z₂₂Self-impedance of node 1, node 2, respectively, Z₁₂And Z₂₁Are both the transimpedance of node 1 and node 2;

2) and calculating admittance matrixes corresponding to the nodes 1 and 2, wherein the admittance matrixes comprise:

wherein, Y_eqDenotes the admittance matrix, Y, corresponding to node 1 and node 2₁₁、Y₂₂Self-admittance, Y, of node 1, respectively node 2₁₂And Y₂₁Are both the transimpedance of node 1 and node 2;

3) calculating equivalent impedance of a single-channel power transmission section, comprising the following steps:

wherein, X_ΣEquivalent impedance of a single-channel power transmission section;

4) assuming that the voltages of the node 1 and the node 2 are both 1, the static stable power transmission capacity P of a single-channel power transmission section_maxCalculated according to the following formula:

wherein E is₁And E₂Representing the voltages at node 1 and node 2, respectively.

The method for evaluating the fracture surface needs to consider not only the normal mode but also the influence after the network topology changes, because the broken line of the fracture surface part may have a great influence on the strength of the fracture surface, which may be a hidden factor for determining the fracture surface weakness program, but an important factor, so the network topology changes need to be considered as an important index.

When the equivalence calculation is carried out on the section, the equivalence calculation under a normal state, an N-1 state and an N-M state needs to be carried out, and the primary screening is carried out on the key faults mainly according to the change among the three states.

Equivalence calculation under Normal conditions

And performing the equivalent calculation under the condition of complete network section, and performing approximate calculation to obtain the whole equivalent impedance as a comparison reference for considering the broken line subsequently.

Equivalence calculation in the N-1 State

And sequentially performing N-1 disconnection on each tie line in the power transmission section, performing equivalent calculation on the system by taking nodes at two ends of other tie lines as ports, wherein the equivalent impedance after calculation is changed, and the change degree of the power transmission capacity after a return line is disconnected can be reflected.

Equivalence calculation in N-M State

And (3) disconnecting the double-circuit line or the multi-circuit line of the power transmission channel with the double-circuit line or the multi-circuit line in the section, and then calculating the equivalent impedance of the ports on two sides of the other channel connecting lines according to the method. For an actual power grid, if a section contains a relatively large number of links, the effect of disconnecting a channel on the whole is not necessarily large, but under the condition of few links, the disconnection of a channel may cause qualitative change and becomes a key factor for limiting the strength of the section.

Aiming at a multi-channel power transmission section, the static stable power transmission capacity of the power transmission section in a normal state, an N-1 state and an N-M state is calculated according to the following processWherein N represents the total loop number of the multi-channel power transmission section, and M represents the loop number of one channel in the multi-channel power transmission section;

1) node numbers on two sides of all power transmission section channels are counted, and nodes with the same node numbers are adopted for combination;

2) calculating an impedance matrix of a multi-channel power transmission section, comprising the following steps:

wherein,impedance matrix, Z, representing a single channel transmission section₁₁、Z₂₂、...、Z_nnSelf-impedance of nodes 1, 2, …, n, respectively, Z₁₂、Z₂₁、...、Z_1n、Z_n1Is the mutual impedance between different nodes;

3) and calculating an admittance matrix corresponding to the node, wherein the admittance matrix comprises the following components:

wherein,representing admittance matrices, Y, to the node₁₁、Y₂₂、...、Y_nnSelf-admittance, Y, of nodes 1, 2, …, n, respectively₁₂、Y₂₁、...、Y_1n、Y_n1Is the mutual impedance between different nodes;

4) calculating equivalent impedance of multi-channel power transmission section

Adding a row and a column in the admittance matrix corresponding to the node, then carrying out elimination calculation on the admittance matrix corresponding to the node, and obtaining an addition row of diagonal elements after calculation, namely the equivalent admittance between the two nodesEquivalent impedance of multi-channel power transmission sectionExpressed as:

5) static stable power transmission capacity of multi-channel power transmission sectionExpressed as:

in step 2, when the load factor of the power transmission section is represented by η, the following are provided:

wherein, P_loadThe actual power of the transmission profile is represented.

In the step 3, the following three basic principles are adopted to screen the transmission sections, and the final weak section is determined in a step-by-step reduction standard mode according to a set load rate fixed value;

(1) in a normal state, a power transmission section with a higher load rate should be reserved;

(2) in the N-1 state, the load rate is changed greatly, and the load rate is higher after N-1, which is reserved;

(3) in the N-M state, the load rate changes more and the load rate after N-M should be higher.

Based on the above principles, the sections to be paid attention to can be quickly given, specifically, the evaluation values adopted may have certain differences for different power grids, but a certain value can be set, and the sections in a certain number range are searched out in a manner of reducing the standard step by step.

After the weak section is preliminarily screened, the method of calculating the static stability limit of the section can be adopted to accurately calculate the static stability limit of the section at the moment, and the basic process is as follows:

and calculating the static stability limit of all the sections, wherein the static stability margin can be calculated at the same time when a circuit is lost.

Calculating the static stability margin, using the static stability limit power and the current power to calculate the static stability margin

Screening is carried out according to the static stability margin, the smaller static stability margin is generally regarded as a weaker section, all sections can be sorted from small to large, and a certain numerical value is set or the first few sections are selected.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (3)

1. The weak section determination method considering the influence of the network topology change on the power transmission capacity is characterized by comprising the following steps of: the method comprises the following steps:

step 1: calculating the static stable power transmission capacity of a power transmission section considering the network topology change;

step 2: calculating the load rate of the power transmission section;

and step 3: screening the power transmission sections according to the influence degree of the network topology change on the power transmission capacity, and determining weak sections;

in the step 1, the power transmission section comprises a single-passA power transmission section and a multi-channel power transmission section; the static stable power transmission capacity of the single-channel power transmission section and the multi-channel power transmission section respectively uses P_maxAnd P'_maxRepresents;

static stable power transmission capacity P of single-channel power transmission section_maxThe calculation process is as follows:

1) calculating the impedance matrix of nodes 1 and 2 on two sides of a single-channel power transmission section, comprising the following steps of:

$Z_{eq}=\left[\begin{array}{cc}{Z}_{11}& Z_{12}\\ Z_{21}& Z_{22}\end{array}\right]---\left(1\right)$

wherein Z is_eqRepresenting the impedance matrix of nodes 1 and 2 on both sides of a single channel transmission section, Z₁₁、Z₂₂Self-impedance of node 1, node 2, respectively, Z₁₂And Z₂₁Are both the transimpedance of node 1 and node 2;

2) and calculating admittance matrixes corresponding to the nodes 1 and 2, wherein the admittance matrixes comprise:

$Y_{eq}=Z_{eq}^{-1}=\left[\begin{array}{cc}{Y}_{11}& Y_{12}\\ Y_{21}& Y_{22}\end{array}\right]---\left(2\right)$

wherein, Y_eqDenotes the admittance matrix, Y, corresponding to node 1 and node 2₁₁、Y₂₂Self-admittance, Y, of node 1, respectively node 2₁₂And Y₂₁Are both the transimpedance of node 1 and node 2;

3) calculating equivalent impedance of a single-channel power transmission section, comprising the following steps:

$X_{\mathrm{\Σ}}=-\frac{1}{Y_{11}+Y_{12}}-\frac{1}{Y_{22}+Y_{21}}+\frac{1}{Y_{12}}---\left(3\right)$

wherein, X_ΣEquivalent impedance of a single-channel power transmission section;

4) assuming that the voltages of the node 1 and the node 2 are both 1, the static stable power transmission capacity P of a single-channel power transmission section_maxCalculated according to the following formula:

$P_{max}=\frac{E_1{E}_2}{X_{\mathrm{\Σ}}}=\frac{1}{X_{\mathrm{\Σ}}}---\left(4\right)$

wherein E is₁And E₂Respectively represent the voltages at node 1 and node 2;

for the multi-channel power transmission section, the static stable power transmission capacity P 'of the power transmission section in a normal state, an N-1 state and an N-M state is calculated according to the following process'_maxWherein N represents the total loop number of the multi-channel power transmission sections, and M represents the loop number of one channel in the multi-channel power transmission sections;

1) node numbers on two sides of all power transmission section channels are counted, and nodes with the same node numbers are adopted for combination;

2) calculating an impedance matrix of a multi-channel power transmission section, comprising the following steps:

$Z_{eq}^{\′}=\left[\begin{array}{cccc}{Z}_{11}& Z_{12}& ...& Z_{1n}\\ Z_{21}& Z_{22}& ...& Z_{2n}\\ \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}\\ Z_{n1}& Z_{n2}& ...& Z_{nn}\end{array}\right]---\left(5\right)$

wherein, Z'_eqImpedance matrix, Z, representing a single channel transmission section₁₁、Z₂₂、…、Z_nnSelf-impedance of nodes 1, 2, …, n, respectively, Z₁₂、Z₂₁、…、Z_1n、Z_n1Is the mutual impedance between different nodes;

3) and calculating an admittance matrix corresponding to the node, wherein the admittance matrix comprises the following components:

$Y_{eq}^{\′}={Z_{eq}^{\′}}^{-1}=\left[\begin{array}{cccc}{Y}_{11}& Y_{12}& ...& Y_{1n}\\ Y_{21}& Y_{22}& ...& Y_{2n}\\ \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}& \begin{array}{c}.\\ .\\ .\end{array}\\ Y_{n1}& Y_{n2}& ...& Y_{nn}\end{array}\right]---\left(6\right)$

wherein, Y'_eqRepresenting admittance matrices, Y, to the node₁₁、Y₂₂、…、Y_nnSelf-admittance, Y, of nodes 1, 2, …, n, respectively₁₂、Y₂₁、…、Y_1n、Y_n1Is the mutual impedance between different nodes;

4) calculating equivalent impedance X 'of multi-channel power transmission section'_Σ；

Adding a row and a column in the admittance matrix corresponding to the node, then carrying out elimination calculation on the admittance matrix corresponding to the node, and obtaining an addition row of diagonal elements after calculation, namely the equivalent admittance y 'between the two nodes'_eqIs equal impedance X 'of multi-channel power transmission section'_ΣExpressed as:

$X_{\mathrm{\Σ}}^{\′}=\frac{1}{y_{eq}^{\′}}---\left(7\right)$

5) static stable power transmission capability P 'of multi-channel power transmission section'_maxExpressed as:

$P_{max}^{\′}=\frac{1}{X_{\mathrm{\Σ}}^{\′}}=y_{eq}^{\′}---\left(8\right).$

2. the method for determining the weak section considering the influence of the network topology change on the power transmission capacity according to claim 1, is characterized in that: in step 2, when the load factor of the power transmission section is represented by η, the following are provided:

$\mathrm{\η}=\frac{P_{load}}{P_{\max }}---\left(9\right)$

wherein, P_loadThe actual power of the transmission profile is represented.

3. The method for determining the weak section considering the influence of the network topology change on the power transmission capacity according to claim 1, is characterized in that: in the step 3, the following three basic principles are adopted to screen the transmission sections, and the final weak section is determined in a step-by-step reduction standard mode according to a set load rate fixed value;

(1) in a normal state, a power transmission section with high load rate should be reserved;

(2) in the N-1 state, the load rate is large in change and the high load rate after N-1 is reserved;

(3) in the N-M state, the load rate changes greatly and the load rate after N-M is high should be preserved.