CN111339624A

CN111339624A - Short-circuit current direct-current component calculation method based on PSASP and EMTP/ATP

Info

Publication number: CN111339624A
Application number: CN201811553716.9A
Authority: CN
Inventors: 李渝; 孙谊媊; 张锋; 文习山; 王衡; 陈小月; 亢朋朋; 樊国伟; 宋朋飞; 印欣; 杨桂兴; 刘德福; 张杏子
Original assignee: Wuhan University WHU; State Grid Xinjiang Electric Power Co Ltd
Current assignee: Wuhan University WHU; State Grid Xinjiang Electric Power Co Ltd
Priority date: 2018-12-19
Filing date: 2018-12-19
Publication date: 2020-06-26
Anticipated expiration: 2038-12-19
Also published as: CN111339624B

Abstract

The invention relates to an electric power modeling and simulation technology, in particular to a short-circuit current direct-current component calculation method based on PSASP and EMTP/ATP, which divides a regional power grid into an internal power grid and an external power grid, sets an analyzed line as the internal power grid, sets other parts as the external power grids, models the internal power grid, and simplifies the external power grids in an equivalent way; a node between the external power grid and the internal power grid is a boundary node; the external power grid equivalence is simplified into a multi-terminal network only with boundary nodes, and the multi-terminal network comprises injection current sources of the boundary nodes, node self-admittance and mutual admittance among the nodes; setting a short-circuit fault by using PSASP software, solving an injection current source and an admittance matrix of a boundary node after the equivalence of an external power grid, establishing an internal power grid and an external power grid model after the equivalence in EMTP/ATP, setting the short-circuit fault, and obtaining a short-circuit current direct-current component from simulation. The method combines the characteristics of the mathematical model of the complex power system network, has accurate and simple and easy calculation result, and is convenient for routine engineering calculation.

Description

Short-circuit current direct-current component calculation method based on PSASP and EMTP/ATP

Technical Field

The invention belongs to the technical field of electric power modeling and simulation, and particularly relates to a short-circuit current direct-current component calculation method based on PSASP and EMTP/ATP.

Background

Along with the development of power systems, the connection between power supplies is tighter and tighter, and the problem of overproof short circuit capacity of the system is more and more prominent. At present, only a periodic component is considered when the current breaking capacity of the circuit breaker is routinely checked in China, the influence of a direct current component on the breaking capacity of the circuit breaker is not considered, but a short-circuit current direct current component has certain influence on normal breaking of the circuit breaker, and especially under the conditions that the breaking capacity margin of the circuit breaker is smaller and smaller, and the attenuation of the short-circuit current direct current component is slower and slower, the attenuation characteristic of the short-circuit current direct current component is accurately and effectively analyzed, so that the short-circuit current of a system can be normally broken through the circuit breaker of a power grid, and the influence on the power supply reliability caused by the failure of breaking due to the overlarge arc energy and electrodynamic force is avoided.

However, the current calculation of the attenuation of the dc component of the short-circuit current has been lacking in methods and tools that are simple and practical in engineering. The short-circuit current calculation standard is more descriptive of the calculation of the periodic component, but the calculation of the decay time constant of the complex network is not specified explicitly. The existing complex network short-circuit current direct-current component calculation methods include a limit frequency method, a two-branch equivalent network method and an equivalent frequency method. The limiting frequency method is only effective when the time constants of all branches are not greatly different; the two-branch method can only process two branches at a time, and the time constant of one branch must be fixed in advance, so that the two-branch method is inconvenient to use in a multi-power mesh network; and the essence of the two is to perform equivalent transformation on the power network described by the power frequency impedance, so that whether the attenuation of the direct current component without the frequency characteristic is correct or not is difficult to determine by using the equivalent impedance under the power frequency to participate in calculation. The equivalent frequency method needs to select corresponding equivalent frequency f according to the look-up table at different concerned moments_cCalculating the equivalent impedance Z_cHowever, the method needs to calculate the equivalent frequency at different moments after the short circuit and calculate the equivalent impedance under the corresponding equivalent frequency, thereby greatly increasing the calculation workload.

The periodic component and the non-periodic component of the short-circuit current, which need to be more accurately researched and calculated and considered to be attenuated, can be subjected to three-phase full-phase modeling by means of electromagnetic transient simulation software EMTP, and then the corresponding direct-current component is separated from the short-circuit full-current instantaneous value waveform obtained through simulation. When the EMTP is used for modeling, the difficulty is that when the number of equivalent power grid nodes reaches thousands, the workload of equivalent calculation is huge, and the equivalence of the power grid outside the region needs to be simplified. According to a traditional power grid equivalence method such as Ward and REI equivalence, when an equivalent power grid is large, nodes to be eliminated by Gaussian elimination elements are too many, the equivalent power grid becomes difficult to solve, all node voltages of the equivalent power grid are involved in the admittance matrix solving process, and the workload is huge. The method and the tool which are simple and practical in engineering are lacked in the calculation of the attenuation of the direct current component of the short-circuit current in China.

Disclosure of Invention

The invention aims to provide a method for calculating a short-circuit current direct-current component of an equivalent network based on PSASP short-circuit fault simulation and EMTP/ATP electromagnetic transient simulation.

In order to achieve the purpose, the invention adopts the technical scheme that: on the basis of a PSASP and EMTP/ATP short-circuit current direct-current component calculation method, a regional power grid is divided into an internal power grid and an external power grid, an analyzed line is set as the internal power grid, the other parts of the regional power grid are the external power grids, modeling is carried out on the internal power grid, and equivalence simplification is carried out on the external power grids; a node between the external power grid and the internal power grid is a boundary node; the external power grid equivalence is simplified into a multi-terminal network only with boundary nodes, and the multi-terminal network comprises an injection current source of the boundary nodes, node self-admittance and mutual admittance among the nodes; setting open circuit and short circuit faults by using PSASP software, solving an injection current source and an admittance matrix of a boundary node, and calculating a short circuit current direct-current component through EMTP/ATP; the method comprises the following steps:

step 1, isolating an internal network from PSASP software in a three-phase disconnection fault mode, and only performing short circuit calculation on an external power grid;

step 2, performing simultaneous three-phase short circuit on all boundary nodes once in PSASP software, calculating to obtain short circuit branch current of each boundary node, and solving an injection current source of a positive sequence network;

step 3, performing three-phase short circuit on each boundary node one by one, calculating and obtaining the positive sequence current of the short circuit branch and the positive sequence voltage of the boundary node through PSASP software, and solving the positive sequence admittance matrix of the boundary node;

step 4, performing single-phase short circuit on the boundary nodes one by one, calculating and obtaining the zero-sequence current of the short-circuit branch and the zero-sequence voltage of the boundary nodes through PSASP software, and solving the zero-sequence admittance matrix of the boundary nodes;

and 5, building an internal power grid model and an equivalent external power grid model in EMTP/ATP according to the injection current source, the positive sequence admittance matrix and the zero sequence admittance matrix of the positive sequence network calculated in the steps 1-4, setting a short-circuit fault, and separating a corresponding direct-current component from the short-circuit full-current instantaneous value waveform.

The invention has the beneficial effects that: the invention utilizes simulation software PSASP to simulate the broken line and the short circuit fault, further obtains an admittance matrix through matrix operation, simplifies the equivalence of a large-scale power grid example, reconstructs a complete equivalent network in an electromagnetic transient simulation program EMTP/ATP, and utilizes the EMTP/ATP to calculate the direct current component of the short circuit current. The calculation amount in the equivalence process is small, the characteristics of a mathematical model of a complex power system network are combined, the calculation result is accurate, simple and feasible, and the routine engineering calculation is facilitated.

Drawings

FIG. 1 is an equivalent network model according to an embodiment of the present invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Electromagnetic transient state analysis is carried out on local lines and nearby areas of a large local power grid by using an electromagnetic transient state simulation program EMTP/ATP, a power grid model with analyzed lines as main bodies needs to be established, and equivalence simplification is carried out on other parts of the power grid. The PSASP software can be widely applied to an electric power system analysis comprehensive program of an electric power department to construct a database of a large-scale network with tens of thousands of nodes, a power grid model associated with an extra-high voltage line is already established, more than 7000 nodes are provided, on the basis, simulation software PSASP is used for carrying out disconnection and short-circuit fault simulation, an admittance matrix is further obtained through matrix operation, equivalence simplification is carried out on a large-scale power grid instance, and a complete equivalent network is reconstructed in an electromagnetic transient simulation program EMTP/ATP. The embodiment provides a short-circuit current direct-current component calculation method based on PSASP and EMTP/ATP.

The regional power grid is divided into an internal power grid and an external power grid, an analyzed line is the internal power grid, detailed modeling is needed, and the external power grid is simplified. The nodes between the external grid and the internal grid are boundary nodes. After the external power grid is subjected to equivalence simplification, the external power grid is a multi-terminal network only with boundary nodes, and the multi-terminal network comprises an injection current source of the boundary nodes, node self-admittance and mutual admittance among the nodes. Setting short-circuit faults in PSASP software to solve an injection current source and an admittance matrix of a boundary node after external power grid equivalence, building an internal power grid model and an external power grid model after equivalence in EMTP/ATP, setting the short-circuit faults, and then separating corresponding direct-current components from short-circuit full-current instantaneous value waveforms obtained through simulation.

Firstly, isolating the internal power grid from PSASP software in the form of three-phase disconnection fault, and only carrying out short circuit calculation on the external power grid. And reserving the network as an internal power grid, and the other networks are external power grids. The internal and external power grids are connected with each other through a plurality of lines, and the operation of the step is finished in a PSASP software in a line disconnection fault operation mode.

And secondly, performing simultaneous three-phase short circuit on all boundary nodes once in PSASP software, and calculating to obtain short circuit branch current of each boundary node. Because the voltage of each boundary node is zero, the short-circuit branch current of each boundary node is equal to the injection current source of the node in the external power grid after the short-circuit branch current is equivalent. Because the equivalent external power grid only has boundary nodes, the injection current source, the positive sequence admittance matrix and the zero sequence admittance matrix of the equivalent boundary nodes of the external power grid need to be solved on the basis of PSASP software short circuit calculation. The general negative sequence network and the zero sequence network are passive networks, and only the injection current source of the positive sequence network needs to be solved.

And thirdly, carrying out three-phase short circuit on each boundary node one by one, calculating by PSASP software to obtain the positive sequence current of the short circuit branch and the positive sequence voltage of the boundary node, respectively ranking node voltage equations of short circuit each time according to the obtained equivalent injected current source of the boundary node in the external positive sequence network, and simultaneously solving to obtain the positive sequence admittance matrix of the boundary node.

And fourthly, performing single-phase short circuit on the boundary nodes one by adopting the same method, calculating and obtaining the zero-sequence current of the short circuit branch and the zero-sequence voltage of the boundary nodes through PSASP software, respectively writing a node voltage equation of each short circuit, and simultaneously solving to obtain a zero-sequence admittance matrix of the boundary nodes. It should be noted that the injection current source of the boundary node is positive sequence, so for the zero sequence network, the injection current source of the boundary node is zero.

And fifthly, building an internal power grid model and an equivalent external power grid model in the EMTP/ATP, setting short-circuit faults, and separating corresponding direct-current components from the short-circuit full-current instantaneous value waveform obtained through simulation.

Taking a power grid with 5-point boundary nodes as an example, the equivalent external power grid network is shown in fig. 1, wherein injection current sources of all nodes are marked

And the admittance of the respective branches. All nodes, legs and related parameters of the equivalent network have been established in the PSASP software.

(1) And removing nodes and branches of the internal power grid of the equivalent network, and reserving a part of the network, namely the external power grid.

(2) The 4

boundary nodes

1, 2, 3, 4, 5 in fig. 1 are simultaneously in metallic short circuit, and the voltage of 5 nodes is zero, and all nodes in the figure are equipotential, so the current of the admittance branch of 4 boundary nodes in fig. 1 is zero. Taking boundary node 1 as an example, y_l0、y₁₂、y₁₃、y₁₄、y₁₅The branch current is zero. The current I of the short-circuit branch can be obtained by PSASP software calculation_f1According to kirchhoff's law of current, this current is equal to the injection current source I₁. The same can obtain the injection current sources of other 2, 3, 4 and 5 boundary nodes.

(3) And (3) carrying out three-phase short circuit on each boundary node one by one, calculating by PSASP software to obtain the positive sequence current of the short circuit branch and the positive sequence voltage of 5 boundary nodes, respectively writing a node voltage equation of each short circuit in a row, and simultaneously solving to obtain the positive sequence admittance matrix of the boundary nodes. Firstly, still taking the boundary node l in fig. 1 as an example, the node l is caused to generate a metallic short circuit, and the positive sequence current I of the short-circuited branch can be obtained through calculation of the PSASP software_f1And positive sequence voltages of 5 boundary nodes, injection current source of each node

The node voltage equation can thus be written as:

wherein: the left 1 st entry of the equal sign is the admittance matrix of the 5 points, self-admittance Y₁₁＝y_l0+y_l2+y_l3+y₁₄+y₁₅Mutual admittance Y₁₂＝-y₁₂，Y₁₃＝-y₁₃，Y₁₄＝-y_14，Y₁₅＝-y_15，(ii) a Item 2 on the left of the equal sign is the voltage of 5 boundary nodes when the boundary node 1 is short-circuited; i is_f1Is node 1 short circuit branch current; the 5-point injection current source is to the right of the equal sign.

Similarly, if the three-phase short circuit calculation is performed at the

nodes

2, 3, 4, and 5, the following are also performed:

the synthesis of (1-1) (1-2) (1-3) (1-4) (1-5) can obtain:

and (4) performing matrix inversion calculation according to the voltage matrix and the current matrix obtained by short circuit calculation in the formula (1-6) to obtain an admittance matrix of the boundary node. The dimension of the matrix operation is equal to the number of boundary nodes, the calculation amount is small, and Matlab software can be adopted to complete the matrix operation.

(4) And (3) performing single-phase short circuit on each boundary node one by one, calculating and obtaining zero sequence current of the short circuit branch and zero sequence voltage of 5 boundary nodes through PSASP software, respectively writing a node voltage equation of each short circuit in a row, and performing simultaneous solution to obtain a zero sequence admittance matrix of the boundary nodes. The injection current source of the boundary node is zero, and the current matrix in the formula (1-6) only contains the zero sequence current of the short-circuit branch.

(5) Injection current source of boundary node after equivalence of internal power grid and external power grid is built in EMTP/ATP

And admittance y₁₀、y₂₀、y₃₀、y₄₀、y₅₀Setting short-circuit fault, and separating corresponding direct current component from short-circuit full current instantaneous value waveform obtained by simulation.

It should be understood that parts of the specification not set forth in detail are well within the prior art.

Although specific embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is only limited by the appended claims.

Claims

1. The short-circuit current direct-current component calculation method is characterized in that a regional power grid is divided into an internal power grid and an external power grid, an analyzed line is set as the internal power grid, the other parts of the regional power grid are the external power grids, the internal power grid is modeled, and the external power grids are subjected to equivalence simplification; a node between the external power grid and the internal power grid is a boundary node; the external power grid equivalence is simplified into a multi-terminal network only with boundary nodes, and the multi-terminal network comprises an injection current source of the boundary nodes, node self-admittance and mutual admittance among the nodes; setting disconnection and short-circuit faults by using PSASP software, solving an injection current source and an admittance matrix of a boundary node, and calculating a short-circuit current direct-current component through EMTP/ATP; the method comprises the following steps: