CN107317326B - Grid regulation current limiting method based on improved REI equivalence - Google Patents

Grid regulation current limiting method based on improved REI equivalence Download PDF

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CN107317326B
CN107317326B CN201710532245.2A CN201710532245A CN107317326B CN 107317326 B CN107317326 B CN 107317326B CN 201710532245 A CN201710532245 A CN 201710532245A CN 107317326 B CN107317326 B CN 107317326B
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equivalence
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rei
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CN107317326A (en
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翁汉琍
惠宇翔
黄景光
魏繁荣
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China Three Gorges University CTGU
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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Abstract

A grid regulation current limiting method based on improved REI equivalence is characterized in that dynamic equivalence improvement is conducted on a conventional REI equivalence method, parameters of equivalent generators are determined through power transmission factor aggregation of each generator on a virtual branch in an equivalence process, then network parameters of a system to be equalized under a short-circuit current exceeding scene are obtained through the method in combination with a line breaking current limiting mechanism, and finally an optimal line breaking combination meeting the current limiting requirement is selected in a research system. The method can quickly find the optimal line breaking scheme without traversing the whole network, has small calculation amount in the equivalence process and high equivalence result precision, can better keep the dynamic characteristics of the original network, and is particularly suitable for online equivalence simplification.

Description

Grid regulation current limiting method based on improved REI equivalence
Technical Field
The invention relates to the field of analysis and calculation of a power system, in particular to a grid regulation current limiting method based on improved REI equivalence.
Background
With the continuous expansion of the scale of the power grid, the power grid connection between areas is increasingly tight, so that the short-circuit current level of the system is also increased year by year, and at present, part of power grid enterprises are tested by the problem of exceeding the standard of the short-circuit current and take corresponding measures. In view of the current limiting effect and the difficulty in engineering implementation, the open circuit is widely used in order to facilitate its implementation without additional cost. In an actual power grid, sites with excessively high short circuit levels are often concentrated in a few areas, and when an optimal disconnection combination scheme is selected, if a full-grid traversal method is selected, time is obviously wasted, and efficiency is reduced.
When a large-scale power network is faced, compared with other equivalent methods, the REI equivalent method has excellent calculation speed and precision and has a better practical application prospect. However, when the internal network is disturbed, the conventional REI cannot keep the dynamic characteristics of the original network, and even the problem that the resistance of the power transmission line is negative occurs, so that a large error inevitably occurs in the equivalence process, and the calculation accuracy is seriously influenced.
Disclosure of Invention
The method aims at the defects that the traditional method is large in calculation amount and the calculation speed cannot meet the online calculation requirement of the power system. The invention provides a grid regulation current-limiting method based on improved REI equivalence, which is applied to a grid regulation current-limiting strategy by improving dynamic equivalence of a conventional REI static equivalence method and combining a line breaking current-limiting mechanism. The method is high in calculation precision, the power grid scale is obviously simplified, and the optimal current-limiting disconnection combination scheme can be selected without traversing the whole power grid.
The technical scheme adopted by the invention is as follows:
a net rack adjusting and current limiting method based on improved REI equivalence comprises the following steps:
step 1: inputting the basic data of the whole network, including topological structure and measurement information, and calculating short-circuit current to obtain n potential standard exceeding sites, so as to obtain the current limiting sensitivity of the branch of the network frame according to the impedance matrix of each node;
step 2: determining the over-standard severity degree according to the over-standard severity degree of the short-circuit current of each over-standard station, and carrying out current limiting weighting according to the over-standard severity degree, so as to obtain the total current limiting sensitivity of any one cut-off branch to the over-standard stations of the whole network, namely the comprehensive current limiting sensitivity of the branch; sequencing branch current limiting sensitivity, dividing an original system into a research system and an external system according to the sequence, determining boundary nodes, and then performing load displacement and bus simplification on the external system;
and step 3: performing equivalence operation on an external system by adopting a conventional REI equivalence method at a boundary node to construct a virtual lossless REI network, grouping according to power angle curves of all generators before equivalence, and defining a ratio of transmission power of a certain generator to be aggregated on a virtual branch to total apparent power of the generator under a tidal current basis as a power distribution factor;
and 4, step 4: the method comprises the steps of introducing generator inertia constants to assist solving of aggregation parameters of an equivalent machine, replacing the inertia constants of a plurality of parallel generators by equivalent inertia constants of the equivalent machine, further estimating relevant parameters of the equivalent machine by utilizing the weight occupied by each inertia constant, realizing REI dynamic equivalence improvement and completing dynamic equivalence operation of an external system;
and 5: and performing branch comprehensive sensitivity sequencing combination on the equivalent system, considering that the short-circuit current level of each station is below an overproof value, and taking the total short-circuit current reduction amount and the structural integrity of the power grid as preferred indexes to obtain an optimal current-limiting disconnection combination scheme.
According to the grid regulation current-limiting method based on the improved REI equivalence, a dynamic equivalence thought is applied on the basis of time domain analysis, and branch current-limiting sensitivity is obtained through the acquisition of real-time data of a system, so that the experience of external system division is avoided; the comprehensive current limiting sensitivity of the branch obtained by weighting according to the severity of each standard exceeding station is more persuasive; the equivalence method is combined with the net rack adjustment strategy, so that the online computing capacity is greatly enhanced; the method is characterized in that a conventional REI static equivalence method is improved, a virtual lossless REI network is formed in the process of processing an external system by the REI equivalence method, power distribution factors are defined, the generator inertia constant is introduced to assist in solving the aggregation parameters of an equivalence machine, the state vector and the characteristic value matrix of the system do not need to be calculated in the equivalence process, and the method is suitable for equivalence simplification of a large-scale power network and has high practical value.
Drawings
Fig. 1 is a flow chart of a net rack adjustment current limiting algorithm based on an improved REI equivalent value.
Fig. 2 is a conventional REI equivalent schematic of the present invention.
FIG. 3 is a schematic diagram of the Kundru test system of the present invention.
FIG. 4 is a schematic diagram of an equivalent post-Kundru test system of the present invention.
FIG. 5 is a rocking curve of the rotating speed of the equivalent front generator according to the present invention.
FIG. 6 is a rocking curve of the rotational speed of the generator after equivalence according to the present invention.
FIG. 7 is a graph of the equivalent pre-node voltage of the present invention.
FIG. 8 is a graph of equivalent post-node voltages for the present invention.
FIG. 9 is a wiring diagram of an equivalent front 39-node system of the present invention.
FIG. 10 is a diagram of equivalent 39-node system wiring of the present invention.
Detailed Description
The present invention will be described in further detail below with reference to two examples and drawings, but the embodiments of the present invention are not limited thereto.
Fig. 1 is a flow chart showing steps of a method for adjusting a current limit of a rack based on an improved REI equivalent according to the present invention. Specifically, the method mainly comprises the following steps:
step 1: and acquiring the basic data of the whole network in real time, performing short circuit calculation, and finding n potential standard exceeding sites. For overproof site m, assume Z'mmThe current value of the breaker is i for m-node self-impedance after the branch circuit is disconnectedmaxWith an over-scalar of △ i ═ im-imax. Then the minimum increment of the self-impedance of the superscalar node is as follows:
Figure BDA0001339563520000031
if any branch i-j (i is not equal to j) of the cut-off network, the self-impedance increment of the node m is as follows:
Figure BDA0001339563520000032
(2) in the formula, zijBranch impedances for lines i-j; zijIs the ith row and the j column of the node impedance matrix; k is the transformation ratio of the transformer branch, and is taken
Figure BDA0001339563520000033
When the line branches, k is 1. Defined according to formula (2) by θij,mIt is re-expressed. Thetaij,mRepresenting the sensitivity of the cut-off branch i-j to the current limiting of the overproof station m, the larger the value of the sensitivity is, the better the corresponding current limiting effect is.
According to the obtained thetaij,mAnd sorting the sizes to determine the disconnection priority of the line. If present
Figure BDA0001339563520000034
The situation shows that the situation that the short-circuit current of the overproof station is not limited to be below the breaking capacity by only opening the lines i-j is not enough, and at the moment, the number of the open lines needs to be increased until the lowest self-impedance increment △ Z is reached, so that the current limiting requirement is met.
Step 2-1: and determining the exceeding severity degree according to the short-circuit current exceeding magnitude of each exceeding station, and carrying out current limiting weighting according to the exceeding severity degree so as to obtain the total current limiting sensitivity of any branch circuit to the total network exceeding stations. From the live operation of a power grid, when a short-circuit current exceeds the standard, more than one current exceeding station is possible, and the current limiting effect on the multiple exceeding stations is considered simultaneously when a circuit is opened. Determining the station exceeding severity according to the current exceeding of each exceeding station:
Figure BDA0001339563520000035
(3) wherein F is a superscalar site set, ifValue of fault current, i, representing station fmaxIs the rated breaking current of the breaker, and r is a constant.
afThe larger the standard deviation is, the more serious the standard deviation scene of the station f is, and according to the standard deviation severity index, the comprehensive current limiting sensitivity of the disconnected branch i-j to the whole system is further obtained:
Figure BDA0001339563520000036
step 2-2: and sequencing the branch current limiting sensitivity, dividing the original system into a research system and an external system according to the sequence, determining boundary nodes, and performing equivalence operation on the external system. The dynamic response process of an external system when the internal system is disturbed is examined by taking the limit short-circuit current as the background, so that the error caused by the conventional static equivalence method is not negligible. And (3) performing dynamic equivalence improvement on the conventional REI equivalence in the high transient fitting property of the REI equivalence method, and applying the improved equivalence method to a current-limiting equivalence strategy.
The main idea of the conventional REI equivalence method is that after nodes in a network are divided into reserved nodes and nodes to be eliminated, active nodes in the nodes to be eliminated are classified according to the properties of the nodes, and then are replaced by a virtual equivalent active node, so that a virtual lossless REI network is constructed, as shown in fig. 2, and finally, the passive network is eliminated by adopting a conventional network simplification method. Briefly set forth below:
before equivalence, the node properties in the external system are classified and grouped, fig. 2 only represents a grouping situation, and a virtual active node R replaces a plurality of active nodes in the external systemAnd the point is connected to the original source node through a lossless REI network. Access yRTo counteract y1～ynThe losses that occur in (a).
Figure BDA0001339563520000041
Figure BDA0001339563520000042
Figure BDA0001339563520000043
Figure BDA0001339563520000044
In the above formula, SiFor the power generation of generator i, ViIs node voltage at node i, R is REI net virtual active node, yiIs the virtual impedance of generator i and node G. The voltage at the point R can be solved by equations (5) and (6) simultaneously. The voltage at the G point is generally set to 0V, and the admittance yRAnd y1～ynThe parameters (C) are easily calculated by the equations (7) and (8).
And step 3: based on the dynamic equivalence improvement of the conventional REI equivalence, the REI equivalence is carried out on an external system at a system boundary node, and the basic steps of simplification are similar to the steps 2-2.
If f is an REI equivalent boundary node, A represents an internal system node, and the system operation except for the f point is only carried out in the equivalent process, and the A and the f are not changed. G1、G2The f-node is an active node of an external system and is in direct or indirect electrical communication with the f-node. z is a radical of1f(z1f) And yf0Respectively equal impedance and parallel admittance.
The load in the grid after the short circuit can be approximately represented by a constant impedance, so that its admittance values can be incorporated into the full-grid admittance matrix in the short circuit calculation. The admittance increment is given by equation (9), and the admittance value is solved by equation (10).
Yl＝diag[Yl,1,…,Yl,k](9)
Figure BDA0001339563520000045
In the above formula, Pl,kAnd Ql,kBeing active and reactive components of the load, Yl,kFor the load admittance value, UkFor load terminal voltage, k is the bus bar designation.
Setting an active node set in a waiting value system as k, a load node set as c, a boundary node set for REI equivalence as f, and r as a node set containing f and k. By the definition, the original system has the following node equation:
Figure BDA0001339563520000051
where I is the load equivalent admittance already incorporated into the network admittance matrixc＝0。
A simple derivation can be found:
Figure BDA0001339563520000052
according to the definition of r, the following are also provided:
Figure BDA0001339563520000053
from equation (11), the injection current of the boundary node can be derived:
Figure BDA0001339563520000054
meanwhile, the parameters of the parallel admittance are as follows:
Figure BDA0001339563520000055
the equivalence finally needs to aggregate a plurality of generators in an external system, so that relevant parameters such as the sub-transient reactance of the equivalent machine are determined. And (4) considering the influence of the inertia constant of the generator on the transient stability of the system, and introducing the inertia constant of the generator to assist in solving. Defining the ratio of the transmission power of a certain generator to be aggregated on a virtual branch circuit to the total apparent power of the generator under the tidal current base as a power distribution factor:
Figure BDA0001339563520000056
(16) in the formula, SjfFor transmission power of generator j to node f, PjThe active power output of the generator j under the tidal current base solution is obtained.
And 4, step 4: and (3) introducing generator inertia constant to assist the solving of the aggregation parameters of the equivalent machine, replacing the inertia constants of a plurality of parallel generators by the equivalent inertia constant of the equivalent machine, further estimating the related parameters of the equivalent machine by utilizing the weight occupied by each inertia constant, realizing the REI dynamic equivalence improvement and finishing the dynamic equivalence operation of an external system.
According to the solution of the power distribution factor in step 3, the apparent power of the aggregated generator at the node g can be obtained as follows:
Figure BDA0001339563520000057
(17) in the formula, SNjFor reference power of external system generator, reference voltage VNjIs the nominal voltage of the boundary node f.
The inertia constants of a plurality of parallel generators are used as the equivalent inertia constant H of an equivalent machinegInstead, according to the essential definition of the inertia constant, it is expressed by a power distribution factor:
Figure BDA0001339563520000061
the inertia constant occupancy weight is used to further estimate equivalent phase related parameters, and here, the sub-transient reactance is taken as an example for explanation, and the resistance, reactance, time constant and the like can be obtained by analogy.
Figure BDA0001339563520000062
In order to verify the effectiveness of the dynamic equivalence method, in example 1, a classical four-engine two-region system in a book of kundur is used as a research object, an original kundur system is shown in fig. 3, a network located in a dotted line is used as an internal system, equivalence operation is performed on an external network, and fig. 4 is a kundur system after dynamic REI equivalence is adopted. Nodes 6x and 10x are equivalent nodes of external system nodes 1,2,5 and 3,4,11 respectively, the generators connected to the two nodes are aggregated equivalent machines, the branches 6-6x and 10-10x are virtual branches assumed in an equivalence process, and the virtual impedance on the branch can be obtained by the methodfg＝0.000204+j0.011913p.u.。
The equivalence effect is evaluated under the system steady state and the time domain dynamic state respectively, and the active power and the voltage amplitude of the boundary nodes 6 and 10 before and after equivalence are given in table 1. A three-phase short-circuit fault disturbance is set at node 8 for 0.08s duration, simulation 5 s. Fig. 5-8 show the oscillation curve of the rotation speed before and after the equivalence and the voltage amplitudes at the nodes 7,8 and 9, and it can be seen that the voltages at the measurement point of the system after the equivalence are completely the same relative to the original system, and the swing curve of the equivalent machine and the original generator is also approximately in the mean value range.
TABLE 1
Figure BDA0001339563520000063
And 5: and 3, performing equivalent operation on the original system, calculating the branch breaking and current limiting sensitivity in the internal system, and sequencing and numbering the branches according to the sensitivity. And (3) performing branch comprehensive sensitivity sequencing combination on the equivalent system, considering that the short-circuit current level of each station is below an overproof value, and finally obtaining an optimal current-limiting disconnection combination scheme by taking the total short-circuit current reduction amount and the structural integrity of the power grid as preferred indexes. The concrete implementation is divided into the following 3 steps:
step 5-1: and (4) performing descending order arrangement on the comprehensive current limiting sensitivity of the branches in the research system, setting the initial broken line number as n, and finding out a candidate broken branch set. And comparing the current limiting effect of each branch circuit to determine whether the safety requirement is met.
Step 5-2: and selecting the branch combination with the maximum comprehensive current limiting sensitivity as the optimal on-off measure under the condition of meeting the current limiting requirement of the system, and finishing the on-off line screening work.
Step 5-3: if Step1 fails, the number of disconnections is set to n +1, and the operation is repeated. And obtaining an optimal disconnection scheme until the current limiting requirement is met.
To explain this procedure in detail with reference to the following embodiments, fig. 8 shows an IEEE-39 node system as a simulation model of embodiment 2, where the voltage class of the system node (excluding the generator node) is set to 220kV, the reference voltage is set to 242kV, and the short-circuit current is limited to 65 pu. And short-circuit calculation is carried out to obtain the superscalar nodes 2, 16 and 39, and the three-phase short-circuit currents of the superscalar nodes respectively reach 71.55pu, 70.26pu and 72.48 pu. And calculating the cut-off current-limiting sensitivity of each branch, and dividing the inside and the outside of the system according to the sensitivity to eliminate branches with non-ideal current-limiting effect of a cut-off line on an over-standard point. In fig. 9, an external equivalent area is divided into three parts and separated by a dotted line, and fig. 10 is a system network after dynamic REI equivalence, which shows that the model size is greatly reduced by applying an equivalence technology in a cut-off line current limiting strategy, and the system after equivalence keeps 22 nodes and 26 branches.
The branch current limiting sensitivity analysis is performed on the post-equivalence system, and the result is shown in table 2. 6 candidate branches which have large influence on each overproof station are given in the table, and the branches are arranged according to the size of the comprehensive current limiting sensitivity of the system in a descending order. In order to ensure that the system is not unstable, the connection line of the generator and the system is not considered in a breakable line. Table 3 shows the specific current limiting effect of the 6 candidate branches, and it can be seen that three out-of-standard sites are not enough to be simultaneously reduced below the threshold of out-of-standard short circuit current under the condition of keeping the single branch open, and the open loop number should be increased at this time to meet the safety requirement.
TABLE 2
Figure BDA0001339563520000071
Specific current limiting effects under the condition of opening and closing the 2-circuit branch are given below a table 3, and the first 3 combination schemes with optimal current limiting effects are screened out. It can be seen that the combined current reduction effect also complies with the comprehensive current limiting sensitivity sequencing of the system, and the effectiveness of the current limiting strategy is verified. Finally, the total amount of the current reduction of the power grid is used for carrying out optimization in a feasible implementation scheme, in the embodiment 2, the branches 16-17 and 1-2 are selected as the optimal combination of the cut-off branches, the result is consistent with that of a system before equivalence, meanwhile, compared with an original current standard exceeding system, the total amount of the current of each standard exceeding station is reduced by 20.91%, and the time consumed in the whole process is 0.32 s.
TABLE 3
Figure BDA0001339563520000072
Figure BDA0001339563520000081
As described above, the present invention can be preferably realized. According to the grid regulation current limiting method based on the REI equivalence method, the inconvenience of a traditional method that a whole network traverses and screens a broken line measure is eliminated, and one current limiting branch circuit pretreatment is carried out before a system is screened, and the simulation result of the embodiment 2 shows that the method not only obviously improves the operation efficiency and saves time consumption, but also ensures higher accuracy, and can correctly select an optimal broken line current limiting combination; the traditional REI static equivalence method is improved, aggregation parameter calculation of an equivalence machine is carried out according to an inertia constant value by using an index of a power distribution factor of each generator on a virtual branch, the reliability of an equivalence effect is verified in the embodiment 1, the equivalence simplification is carried out on a system by using the improved REI dynamic equivalence method, the network retains the dynamic characteristics of the original network after equivalence, and the equivalence effect is good; the REI dynamic equivalence improving method does not need to calculate a state vector and a characteristic value matrix of a system in the process, and is suitable for equivalence simplification of a large-scale power network.

Claims (4)

1. A net rack adjusting and current limiting method based on improved REI equivalence is characterized by comprising the following steps:
step 1: inputting the basic data of the whole network, including topological structure and measurement information, and calculating short-circuit current to obtain n potential standard exceeding sites, so as to obtain the current limiting sensitivity of the branch of the network frame according to the impedance matrix of each node;
step 2: determining the over-standard severity degree according to the over-standard severity degree of the short-circuit current of each over-standard station, and carrying out current limiting weighting according to the over-standard severity degree, so as to obtain the total current limiting sensitivity of any one cut-off branch to the over-standard stations of the whole network, namely the comprehensive current limiting sensitivity of the branch; sequencing branch current limiting sensitivity, dividing an original system into a research system and an external system according to the sequence, determining boundary nodes, and then performing load displacement and bus simplification on the external system;
and step 3: performing equivalence operation on an external system by adopting a conventional REI equivalence method at a boundary node to construct a virtual lossless REI network, grouping according to power angle curves of all generators before equivalence, and defining a ratio of transmission power of a certain generator to be aggregated on a virtual branch to total apparent power of the generator under a tidal current basis as a power distribution factor;
and 4, step 4: the method comprises the steps of introducing generator inertia constants to assist solving of aggregation parameters of an equivalent machine, replacing the inertia constants of a plurality of parallel generators by equivalent inertia constants of the equivalent machine, further estimating relevant parameters of the equivalent machine by utilizing the weight occupied by each inertia constant, realizing REI dynamic equivalence improvement and completing dynamic equivalence operation of an external system;
and 5: and performing branch comprehensive sensitivity sequencing combination on the equivalent system, considering that the short-circuit current level of each station is below an overproof value, and taking the total short-circuit current reduction amount and the structural integrity of the power grid as preferred indexes to obtain an optimal current-limiting disconnection combination scheme.
2. The grid regulation current limiting method based on the improved REI equivalence as claimed in claim 1, wherein: in the step 3 and the step 4, the dynamic equivalence improvement method for the conventional REI equivalence method is as follows:
if f is an REI equivalent boundary node, A represents an internal system node, the system except the f point is only operated in the equivalence process, and the A and the f are not operatedIs pre-varied, G1、G2The f node is an active node of an external system and is in direct or indirect electrical communication with the f node; z is a radical of1fAnd yf0Respectively equal impedance and parallel admittance;
the load in the power grid after short circuit is approximately expressed by constant impedance, so that the admittance value of the power grid is merged into a whole-grid admittance matrix during short circuit calculation, and the admittance increment and the admittance value are obtained by applying the following formula:
Yl＝diag[Yl,1,…,Yl,k]；
Figure FDA0002368424980000011
wherein: pl,kAnd Ql,kBeing active and reactive components of the load, Yl,kFor the load admittance value, UkK is a load end voltage, and k is an active node set label;
the label of an active node set in a waiting value system is set as k, a load node set is set as c, a boundary node set for REI equivalence is set as f, r is a node set containing f and k, and the following node equations are provided for the original system through the definition:
Figure FDA0002368424980000021
since the load equivalent admittance has been incorporated into the network admittance matrix, IcWhen the value is 0, the following components are available:
Figure FDA0002368424980000022
according to the definition of r, the following are also provided:
Figure FDA0002368424980000023
obtaining the injection current of the boundary node:
Figure FDA0002368424980000024
meanwhile, the parameters of the parallel admittance are as follows:
Figure FDA0002368424980000025
and finally, the equivalence needs to aggregate a plurality of generators in an external system, so that the secondary transient reactance related parameters of an equivalent machine are determined, the influence of the inertia constant of the generator on the transient stability of the system is considered, the inertia constant of the generator is introduced for assisting in solving, and the ratio of the transmission power of a certain generator to be aggregated on a virtual branch to the total apparent power of the generator under the tidal current basis is defined as a power distribution factor:
Figure FDA0002368424980000026
in the above formula, SjfFor transmission power of generator j to node f, PjThe active power output of the generator j under the tidal current base solution;
from the solution of the above power distribution factors, the apparent power of the aggregate generator at node g can be derived:
Figure FDA0002368424980000027
in the above formula, SNjA reference power for an external system generator;
the inertia constants of a plurality of parallel generators are used as the equivalent inertia constant H of an equivalent machinegInstead, according to the essential definition of the inertia constant, it is expressed by a power distribution factor:
Figure FDA0002368424980000028
further estimating related parameters of the equivalent machine, and the sub-transient reactance x' of the equivalent machine by using the inertia constant occupancy weightdgComprises the following steps:
Figure FDA0002368424980000031
the resistance, transient reactance, and time constant of the equivalent machine can be obtained by analogy.
3. A net rack adjusting and current limiting method based on improved REI equivalence is characterized by comprising the following steps:
step 1: acquiring all-network basic data in real time, performing short circuit calculation, finding n potential overproof sites, and assuming Z 'for the overproof sites m'mmThe current value of the breaker is i for m-node self-impedance after the branch circuit is disconnectedmaxWith an over-scalar of △ i ═ im-imaxAnd then the minimum increment of the self-impedance of the superscalar node is as follows:
Figure FDA0002368424980000032
if any branch i-j, i ≠ j of the cut-off network, the self-impedance increment of the node m is as follows:
Figure FDA0002368424980000033
(2) in the formula, zijBranch impedances for lines i-j; zijIs the ith row and the j column of the node impedance matrix; k is the transformation ratio of the transformer branch, and is taken
Figure FDA0002368424980000034
When the line is branched, k is 1; defined according to formula (2) by θij,mTo re-express it, thetaij,mRepresenting the sensitivity of the cut-off branch i-j to the current limiting of the overproof station m, wherein the larger the value of the sensitivity is, the better the corresponding current limiting effect is;
according to the obtained thetaij,mSorting the sizes, determining the line disconnection priority, if any
Figure FDA0002368424980000035
The situation shows that the short-circuit current of the superstandard station is not limited to be below the interruption capacity by only opening the lines i-j, and at the moment, the number of the opening lines needs to be increased until the lowest self-impedance increment △ Z is reached, so that the current limiting requirement is met;
step 2-1: the superstandard severity degree is determined according to the superstandard severity degree, current limiting weighting is carried out according to the superstandard severity degree, further, the total current limiting sensitivity of any branch circuit to the superstandard stations of the whole network is obtained, the live operation of the power grid is seen, when the short-circuit current exceeds the standard scene, more than one superstandard station is provided, the current limiting effect to a plurality of superstandard stations is considered simultaneously by a cut-off circuit, and the superstandard severity degree of the stations is determined according to the superstandard current of each superstandard station:
Figure FDA0002368424980000036
(3) wherein F is a superscalar site set, ifValue of fault current, i, representing station fmaxIs the rated breaking current of the breaker, and r is a constant;
afthe larger the standard deviation is, the more serious the standard deviation scene of the station f is, and according to the standard deviation severity index, the comprehensive current limiting sensitivity of the disconnected branch i-j to the whole system is further obtained:
Figure FDA0002368424980000041
step 2-2: sorting the branch current limiting sensitivity, dividing an original system into a research system and an external system according to the sequence, determining boundary nodes, and performing equivalence operation on the external system; on the background of limiting short-circuit current, the dynamic response process of an external system when an internal system is disturbed is inspected, so that errors caused by a conventional static equivalence method are not negligible, the dynamic equivalence improvement is carried out on the conventional REI equivalence between the high transient fitting performance of the REI equivalence method, and the improved equivalence method is used for a current-limiting equivalence strategy;
the conventional REI equivalence method is that after nodes in a network are divided into reserved nodes and nodes to be eliminated, active nodes in the nodes to be eliminated are classified according to the properties of the active nodes, and then a virtual equivalent active node is used for replacing the active nodes, so that a virtual lossless REI network is constructed, and finally the virtual lossless REI network is eliminated by adopting a conventional network simplification method, and the method specifically comprises the following steps:
before equivalence, the node properties in the external system are classified and grouped, a virtual active node R replaces a plurality of original active nodes in the external system, and the virtual active node R is connected to the original active nodes through a lossless REI network and is connected to yRTo counteract y1～ynThe losses generated in (a);
Figure FDA0002368424980000042
Figure FDA0002368424980000043
Figure FDA0002368424980000044
Figure FDA0002368424980000045
in the above formula, SiFor the power generation of generator i, ViIs node voltage at node i, R is REI net virtual active node, yiIs the virtual impedance of generator i and node G; the voltage at the R point is solved by the equations (5) and (6) simultaneously; g point voltage is set to 0V, admittance yRAnd y1～ynThe parameters of (A) are easily calculated by the formulas (7) and (8);
and step 3: based on the dynamic equivalence improvement of the conventional REI equivalence, the REI equivalence is carried out on an external system at a system boundary node, and the basic steps and the method are simplified in the same step 2-2;
if f is REI equivalent boundary node, A represents internal system node, the system operation except f point is only performed in the equivalent process, the A and f are not changed, G1、G2For external systemsThe f node is in direct or indirect electrical communication with the active node of (1); z is a radical of1fAnd yf0Respectively equal impedance and parallel admittance;
the load in the power grid after the short circuit is approximately represented by constant impedance, so the admittance value is incorporated into the whole grid admittance matrix during the short circuit calculation, the admittance increment is given by an equation (9), and the admittance value is solved by an equation (10):
Yl＝diag[Yl,1,…,Yl,k](9)
Figure FDA0002368424980000051
in the above formula, Pl,kAnd Ql,kBeing active and reactive components of the load, Yl,kFor the load admittance value, UkIs the load end voltage, k is the bus label;
setting an active node set in a waiting value system as k, a load node set as c, a boundary node set for REI equivalence as f, and r as a node set containing f and k, and by the above definition, the following node equations are provided for the original system:
Figure FDA0002368424980000052
in the formula: since the load equivalent admittance has been incorporated into the network admittance matrix, Ic＝0；
A simple derivation can be found:
Figure FDA0002368424980000053
according to the definition of r, the following are also provided:
Figure FDA0002368424980000054
from equation (11), the injection current of the boundary node can be derived:
Figure FDA0002368424980000055
meanwhile, the parameters of the parallel admittance are as follows:
Figure FDA0002368424980000056
and finally, the equivalence needs to aggregate a plurality of generators in an external system, so that the secondary transient reactance related parameters of an equivalent machine are determined, the influence of the inertia constant of the generator on the transient stability of the system is considered, the inertia constant of the generator is introduced for assisting in solving, and the ratio of the transmission power of a certain generator to be aggregated on a virtual branch to the total apparent power of the generator under the tidal current basis is defined as a power distribution factor:
Figure FDA0002368424980000057
(16) in the formula, SjfFor transmission power of generator j to node f, PjThe active power output of the generator j under the tidal current base solution;
and 4, step 4: the method comprises the steps of introducing generator inertia constants to assist solving of aggregation parameters of an equivalent machine, replacing the inertia constants of a plurality of parallel generators by equivalent inertia constants of the equivalent machine, further estimating relevant parameters of the equivalent machine by utilizing the weight occupied by each inertia constant, realizing REI dynamic equivalence improvement and completing dynamic equivalence operation of an external system;
according to the solution of the power distribution factor in step 3, the apparent power of the aggregated generator at the node g can be obtained as follows:
Figure FDA0002368424980000058
(17) in the formula, SNjA reference power for an external system generator;
the inertia constants of a plurality of parallel generators are used as the equivalent inertia constant H of an equivalent machinegInstead, according to the essential definition of the inertia constant, it is expressed by a power distribution factor:
Figure FDA0002368424980000061
further estimating related parameters of the equivalent machine, and the sub-transient reactance x' of the equivalent machine by using the inertia constant occupancy weightdgComprises the following steps:
Figure FDA0002368424980000062
the resistance, transient reactance and time constant of the equivalent machine can be obtained by analogy;
and 5: and 3, performing equivalence operation on the original system, calculating branch breaking and current limiting sensitivity in the internal system, sequencing and numbering the branches according to the sensitivity, performing branch comprehensive sensitivity sequencing combination on the system after equivalence, considering that the short-circuit current level of each station is below an over-standard value, and finally taking the total short-circuit current reduction amount and the structural integrity of the power grid as preferred indexes to obtain an optimal current limiting and disconnection combination scheme.
4. The grid regulation current limiting method based on the improved REI equivalence as claimed in claim 3, wherein the step 5 comprises the following steps:
step 5-1: arranging comprehensive current limiting sensitivity of branches in a research system in a descending order, setting the initial broken line number as n, finding a candidate broken branch set, comparing the current limiting effect of each branch, and verifying whether the safety requirement is met;
step 5-2: under the condition of meeting the current limiting requirement of a system, selecting a branch combination with the maximum comprehensive current limiting sensitivity as an optimal cut-off measure to complete the cut-off line screening work;
step 5-3: and if the step 5-1 can not pass through, setting the number of the broken lines as n +1, returning to the repeated operation until the current limiting requirement is met, and obtaining the optimal broken line scheme.
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