CN108092299B

CN108092299B - Method and device for establishing homopolar cross-over fault model between direct current systems

Info

Publication number: CN108092299B
Application number: CN201810006011.9A
Authority: CN
Inventors: 王长香; 张帆; 甄鸿越; 周挺辉; 张东辉; 戴仲覆
Original assignee: CSG Electric Power Research Institute; Power Grid Technology Research Center of China Southern Power Grid Co Ltd
Current assignee: Research Institute of Southern Power Grid Co Ltd
Priority date: 2018-01-03
Filing date: 2018-01-03
Publication date: 2020-03-24
Anticipated expiration: 2038-01-03
Also published as: CN108092299A

Abstract

The embodiment of the invention provides a method and a device for establishing a homopolar cross-over fault model between direct current systems, relates to the field of power systems, and can establish an equivalent model of homopolar cross-over ground faults between the direct current systems. The method comprises the following steps: obtaining a homopolar cross-over ground fault model by utilizing thevenin equivalence; simulating the ground fault model to obtain a fault network topological graph; establishing a fault boundary equation set according to a fault network topological graph and a preset rule; acquiring a trigger angle value of the converter station in the fault network topological graph according to the simulation result of the ground fault model; establishing a homopolar cross-over earth fault equivalent model according to an electromechanical transient simulation rule; and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over ground fault according to the trigger angle value of the converter station in the fault network topological graph, the fault boundary equation set and the preset rectification side equation set.

Description

Method and device for establishing homopolar cross-over fault model between direct current systems

Technical Field

The invention relates to the field of power system analysis, in particular to a method and a device for establishing a homopolar cross-over fault model between direct current systems.

Background

The advantages of direct current engineering in power transmission are obvious, and in recent years, direct current power transmission is mostly adopted in large-capacity long-distance power transmission in China. According to the planning, a large amount of long-distance high-voltage direct-current transmission projects are still operated and built in the future. Because the main energy bases and the load centers in China are reversely distributed, the planned power transmission lines are mostly in the south-north or east-west directions. With the increase of the number of lines, the situation of cross-over of the direct current and the direct current transmission line is inevitable, and the probability of short-circuit fault of the cross-over of the direct current and the direct current is increased. The direct current-direct current cross-over is a complex fault type, and particularly when direct current lines of different voltage levels have cross-over faults, a rectification valve and an inversion valve of a fault pole of a certain return direct current line are completely turned off, and the fault pole is locked and stops running. Therefore, the research on the fault characteristics of the DC-DC cross fault and the fault analysis method have very important guiding significance on the configuration of the DC line protection. The electromagnetic transient simulation can simulate the detailed dynamic process of direct current and a control system thereof in detail, but the calculation scale and the calculation time required by the integral electromagnetic transient simulation are large; the electromechanical transient simulation is an important content of safety and stability analysis and calculation of a power system, and the application of the electromechanical transient simulation relates to the whole power production process such as power grid planning, scheduling, mode making, post inversion analysis and the like, so that a direct current-direct current cross-over fault analysis and calculation method suitable for electromechanical transient simulation is needed to be researched.

However, in the prior art, there is only an overall research and analysis on the dc-dc cross-over ground fault, and an analysis method for a dc system, whether a traveling wave theory or a switching function method, is difficult to apply to the dc-dc cross-over electromechanical transient analysis, and cannot meet the analysis requirement on the dc-dc cross-over ground fault in engineering.

Disclosure of Invention

The embodiment of the invention provides a method and a device for establishing a homopolar cross-over fault model between direct current systems, which are used for realizing electromechanical transient analysis of homopolar cross-over ground faults between direct current transmission systems with different voltage levels.

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

the method comprises the steps that a first direct current system and a second direct current system are included in the direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line are of the same polarity, and the crossover point is grounded; the method comprises the following steps:

performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

carrying out simulation operation on the homopolar crossing earth fault model and acquiring a fault network topological graph according to the simulation operation result of the homopolar crossing earth fault model; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage;

establishing a fault boundary equation set for the fault network topological graph according to a preset rule;

acquiring a trigger angle value of a converter station in a fault network topological graph according to a simulation operation result of a homopolar crossing earth fault model, wherein the converter station comprises a rectifier station;

grounding buses on the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over grounding fault equivalent model;

and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over earth fault in the fault stage according to the trigger angle value of the converter station in the fault network topological diagram, the fault boundary equation set and the preset rectification side equation set.

Optionally, performing single-port thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system includes:

performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

and constructing a homopolar cross-over ground fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

Optionally, obtaining the fault network topology according to the result of the simulation operation of the homopolar crossing-over ground fault model includes:

acquiring current simulation curves of all converter stations in the same-polarity cross-over ground fault model after the same-polarity cross-over ground fault model is subjected to simulation operation;

and acquiring a fault network topological graph according to current simulation curves of all converter stations in the same-polarity cross-over earth fault model.

Further optionally, the obtaining of the firing angle value of the converter station in the fault network topology according to the result of the simulation operation of the homopolar crossing-over ground fault model includes:

acquiring trigger angle simulation curves of all converter stations in the same-polarity cross-over ground fault model after the same-polarity cross-over ground fault model is subjected to simulation operation;

selecting current simulation curves of the converter stations in the fault network topological graph from current simulation curves of all converter stations in the same-polarity cross-over ground fault model, and selecting trigger angle simulation curves of the converter stations in the fault network topological graph from trigger angle simulation curves of all converter stations in the same-polarity cross-over ground fault model;

acquiring a first moment when the current is maximum in a fault stage in a current simulation curve of each converter station in a fault network topological graph; and selecting all the trigger angle values at the first moment in the trigger angle simulation curve of the first converter station in the fault network topology map as the trigger angle values of the first converter station, wherein the first converter station is any converter station in the fault network topology map.

Optionally, calculating a value of the equivalent impedance of the equivalent model of the same polarity cross-over ground fault at the fault stage according to the trigger angle value of the converter station in the fault network topology, the fault boundary equation set and the preset rectification side equation set includes:

calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the equivalent model of the same polarity crossing ground fault at the fault stage according to a trigger angle value, a fault boundary equation set and a preset rectification side equation set of the converter station in the fault network topological graph;

and calculating the value of the fault equivalent impedance of the same-polarity cross-over ground fault equivalent model at the fault stage according to the voltage value and the current value of the bus corresponding to the fault equivalent impedance of the same-polarity cross-over ground fault equivalent model at the fault stage.

In a second aspect, a dc system is provided, which includes a first dc system and a second dc system, where the first dc system is a bipolar two-terminal dc transmission system of a first voltage class, the second dc system is a bipolar two-terminal dc transmission system of a second voltage class, a first transmission line of the first dc system and a second transmission line of the second dc system are bridged at a predetermined crossover point, the first transmission line and the second transmission line have the same polarity, and the crossover point is grounded; the device includes: the system comprises a model building module, a simulation module and a processing module;

the model establishing module is used for performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over grounding fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the simulation module is used for carrying out simulation operation on the homopolar cross-over grounding fault model established by the model establishing module;

the model building module is also used for acquiring a fault network topological graph according to a simulation result of the simulation module after the homopolar cross-over ground fault model is subjected to simulation operation; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage;

the processing module is used for establishing a fault boundary equation set for the fault network topological graph acquired by the model establishing module according to a preset rule;

the processing module is also used for acquiring the trigger angle value of the converter station in the fault network topological graph acquired by the model establishing module according to the simulation operation result of the simulation module on the homopolar crossing earth fault model;

the model establishing module is also used for grounding buses at the rectification side and the inversion side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over grounding fault equivalent model;

the processing module is further used for calculating the value of the fault equivalent impedance of the same polarity cross-over grounding fault equivalent model established by the model establishing module according to the trigger angle value of the converter station in the fault network topological graph, the fault boundary equation set and the preset rectification side equation set in the fault network topological graph in the fault stage.

Optionally, the model building module is specifically configured to: performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system; and constructing a homopolar cross-over ground fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

Optionally, the simulation module is specifically configured to obtain current simulation curves of all converter stations in the same-polarity cross-over ground fault model after performing simulation operation on the same-polarity cross-over ground fault model established by the model establishing module; the model establishing module is used for acquiring a fault network topological graph according to the current simulation curves of all converter stations in the same-polarity cross-over earth fault model acquired by the simulation module.

Optionally, the simulation module is configured to perform simulation operation on the same-polarity cross-over ground fault model established by the model establishing module, and then obtain firing angle simulation curves of all converter stations in the same-polarity cross-over ground fault model;

the processing module is used for selecting current simulation curves of the converter stations in the fault network topological graph from the current simulation curves of all the converter stations in the same-polarity crossing ground fault model acquired by the simulation module, and selecting trigger angle simulation curves of the converter stations in the fault network topological graph from the trigger angle simulation curves of all the converter stations in the same-polarity crossing ground fault model;

acquiring a first moment when the current is maximum in a fault stage in a current simulation curve of each converter station in a fault network topological graph;

and selecting all the trigger angle values at the first moment in the trigger angle simulation curve of the first converter station in the fault network topology map as the trigger angle values of the first converter station, wherein the first converter station is any converter station in the fault network topology map.

Optionally, the processing module is specifically configured to: according to a trigger angle value of a converter station in a fault network topological graph, a fault boundary equation set and a preset rectification side equation set, calculating a voltage value and a current value of a bus corresponding to fault equivalent impedance of a same polarity cross-over ground fault equivalent model established by a model establishing module at a fault stage;

The method and the device for establishing the homopolar cross-over fault model between the direct current systems provided by the embodiment of the invention comprise a first direct current system and a second direct current system, wherein the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is grounded; the method comprises the following steps: performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; carrying out simulation operation on the homopolar crossing earth fault model and acquiring a fault network topological graph according to the simulation operation result of the homopolar crossing earth fault model; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage; establishing a fault boundary equation set for the fault network topological graph according to a preset rule; acquiring a trigger angle value of a converter station in a fault network topological graph according to a simulation operation result of a homopolar crossing earth fault model, wherein the converter station comprises a rectifier station; grounding buses on the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over grounding fault equivalent model; and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over earth fault in the fault stage according to the trigger angle value of the converter station in the fault network topological diagram, the fault boundary equation set and the preset rectification side equation set. According to the technical scheme provided by the embodiment of the invention, firstly, a homopolar cross-over earth fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in a fault stage and a current curve and a trigger angle curve of each converter station in the homopolar cross-over earth fault model are obtained according to a simulation result of the homopolar cross-over earth fault model, and then a boundary equation set related to the current and the voltage of the converter station can be obtained according to a preset rule according to the fault network topological graph, and the trigger angle of the converter station in the fault network topological graph is obtained according to the current curve and the trigger angle curve; finally, according to a trigger angle of a converter station in a network topological graph at a fault stage, a boundary equation set of each network topological graph and a preset rectifying side equation set, calculating a value of a fault impedance equivalence in the fault stage in a homopolar cross-over grounding fault equivalence model which can be used for electromechanical transient simulation by grounding a rectifying side bus and an inverting side bus of a bipolar line with a short-circuit fault in the homopolar cross-over grounding fault model in a homopolar cross-over grounding fault equivalence model according to an electromechanical transient simulation rule; and finally, combining known element parameters obtained from the homopolar cross-over ground fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ground fault equivalent model for analyzing homopolar cross-over ground faults between different direct current systems.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of a method for establishing a homopolar cross-over fault model between dc systems according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a same-polarity cross-over ground fault model according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of an equivalent model of a homopolar cross-over ground fault according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a quasi-steady-state model structure for electromechanical transient simulation analysis according to an embodiment of the present invention;

fig. 5 is a schematic flow chart of a method for establishing a homopolar crossing fault model between dc systems according to another embodiment of the present invention;

fig. 6 is a topology diagram of a fault network according to an embodiment of the present invention;

fig. 7 is a schematic structural diagram of an apparatus for establishing a homopolar crossing fault model between dc systems according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that, in the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "e.g.," an embodiment of the present invention is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present concepts related in a concrete fashion.

It should be noted that, in the embodiments of the present invention, "of", "corresponding" and "corresponding" may be sometimes used in combination, and it should be noted that, when the difference is not emphasized, the intended meaning is consistent.

For the convenience of clearly describing the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second", and the like are used for distinguishing the same items or similar items with basically the same functions and actions, and those skilled in the art can understand that the words "first", "second", and the like are not limited in number or execution order.

In the prior art, there is little overall research and analysis on the dc-dc cross-over fault, and an analysis method for a dc system, whether a traveling wave theory or a switching function method, is difficult to apply to the dc-dc cross-over electromechanical transient analysis, and cannot meet the analysis requirement on the dc-dc cross-over ground fault in engineering.

In view of the above problem, referring to fig. 1, an embodiment of the present invention provides a method for establishing a homopolar crossing fault model between dc systems, including:

101. and performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system.

Specifically, the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, the first voltage level is different from the second voltage level, a first power transmission line of the first direct current system is bridged over a second power transmission line of the second direct current system at a preset crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is grounded; the crossover point refers to a point at which the first direct current transmission line and the second direct current transmission line are short-circuited, and actually, one crossover point is arranged in each of the first direct current transmission line and the second direct current transmission line;

for example, a homopolar cross-over ground fault model is shown with reference to fig. 2, where the dc voltage level of the first dc system is ± UdH, the dc voltage level of the second dc system is ± UdL, UdH is greater than UdL, S1 and S2 are thevenin equivalent power sources of the two ports after thevenin equivalent of the first dc system, S3 and S4 are thevenin equivalent power sources of the two ports after thevenin equivalent of the second dc system, Zeq1 and Zeq2 are thevenin equivalent impedances of the two ports after thevenin equivalent of the first dc system, Zeq3 and Zeq4 are thevenin equivalent impedances of the two ports after thevenin equivalent of the second dc system, T11, T12, T21, T22 are the converter transformers of the first dc system, T31, T32, T41, T42 are the converter transformers of the first dc system, Rec11 and Rec 639 are the converter transformers of the first dc system, and the rectifier station 8653 is the rectifier station of the Rec 21, inv41 and Inv42 are inversion stations of a second direct current system, R11, R12, R21 and R22 are direct current line resistors of a first direct current system, R31, R32, R41 and R42 are direct current line resistors of the second direct current system, a first power transmission line is a positive polarity line in the first direct current system, a second power transmission line is a positive polarity line in the second direct current system, a crossover point on the first power transmission line is f1, a crossover point on the second power transmission line is f2, and f1 and f2 are connected in a ground bridge manner; in practice, the homopolar crossing ground fault only appears in the positive polarity line of the two dc systems, but also in the negative polarity line of the two dc systems.

102. And carrying out simulation operation on the homopolar crossing earth fault model and acquiring a fault network topological graph according to the simulation operation result of the homopolar crossing earth fault model.

Specifically, when the same-polarity crossing ground fault occurs between the direct current systems with different voltage levels, the first power transmission line and the second power transmission line are directly grounded through a crossover point, and when the same-polarity crossing ground fault occurs between the direct current systems with different voltage levels, only one fault stage exists; then, in order to better study the change of the control part (the rectifier station and the inverter station) in the fault, a network topology model which is a simplified model of the fault stage needs to be established, and the fault network topology map is a simplified model of a homopolar cross-over grounding fault model which comprises the current-passing converter station and the line resistance of the first transmission line and the second transmission line in the fault stage.

103. And establishing a fault boundary equation set for the fault network topological graph according to a preset rule.

Specifically, the preset rule herein refers to an equation establishment rule set in the program according to Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL).

104. And acquiring a trigger angle value of a converter station in a fault network topological graph according to a simulation operation result of the homopolar crossing earth fault model, wherein the converter station comprises a rectifier station.

The converter station comprises a rectifier station, and the specific trigger angle value is obtained by extracting according to a simulation curve obtained by simulation.

105. And according to an electromechanical transient simulation rule, grounding buses on the rectification side and the inversion side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance to generate a same-polarity cross-over grounding fault equivalent model.

Specifically, when a cross-over fault occurs between the dc systems, the dc systems may be simulated by using dc blocking and connecting an equivalent impedance in parallel at the converter bus in an electromechanical transient simulation, for example, the equivalent model of the same-polarity cross-over ground fault transformed according to the above rule in fig. 2 is shown in fig. 3, where Z11 replaces the converter transformer T11, the rectifier station Rec11 and the line resistor R11 in the first transmission line in fig. 2, Z12 replaces the converter transformer T21, the inverter station Inv21 and the line resistor R21 in the first transmission line in fig. 2, Z31 replaces the converter transformer T31, the inverter station Rec31 and the line resistor R31 in the second transmission line in fig. 2, and Z12 replaces the converter transformer T41, the inverter station Inv41 and the line resistor R41 in the second transmission line in fig. 2.

106. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over grounding fault at the fault stage according to the trigger angle value of the converter station in the fault network topological diagram, the first boundary equation set and the preset rectification side equation set.

Specifically, in the electromechanical transient simulation analysis of the alternating current-direct current system, a quasi-steady-state model is adopted in the direct current system converter station, which is shown in fig. 4, and each parameter in the rectifier station circuit with the structure shown in fig. 4 meets the following preset rectifier side equation set formula:

presetting a rectification side equation set:

wherein E is_sr、

For the amplitude and angle of the effective value of the rectification side Thevenin equivalent voltage source potential,

Z_eqr、

for the amplitude and angle of the rectification side thevenin equivalent impedance,

E_busr、

for rectifying the amplitude and angle of the primary side bus voltage of the side converter,

I_busr、

the effective value and the angle of the current injected into the direct current system for the primary side bus of the rectifier side converter transformer,

U_dr、I_drfor rectifying side DC voltage and current α_r、μ_rThe angle is a rectification side direct current trigger angle and a commutation overlap angle; x_cr、k_rThe phase change reactance and the phase change transformation ratio are obtained; the subscript r for each of the above parameters represents the rectification side.

It should be noted that the preset rectification side equation set is used for obtaining the parameter values of the rectification station circuit (rectification side).

According to the technical scheme provided by the embodiment, firstly, a homopolar cross-over earth fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in a fault stage and current curves and trigger angle curves of all converter stations in the homopolar cross-over earth fault model are obtained according to a simulation result of the homopolar cross-over earth fault model, and then a boundary equation set related to current and voltage of the converter stations can be obtained according to a preset rule according to the fault network topological graph, and trigger angles of the converter stations in the fault network topological graph are obtained according to the current curves and the trigger angle curves; finally, according to a trigger angle of a converter station in a network topological graph at a fault stage, a boundary equation set of each network topological graph and a preset rectifying side equation set, calculating a value of a fault impedance equivalence in the fault stage in a homopolar cross-over grounding fault equivalence model which can be used for electromechanical transient simulation by grounding a rectifying side bus and an inverting side bus of a bipolar line with a short-circuit fault in the homopolar cross-over grounding fault model in a homopolar cross-over grounding fault equivalence model according to an electromechanical transient simulation rule; and finally, combining known element parameters obtained from the homopolar cross-over ground fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ground fault equivalent model for analyzing homopolar cross-over ground faults between different direct current systems.

Referring to fig. 5, an embodiment of the present invention further provides a method for establishing a homopolar crossing fault model between dc systems as a supplement to the technical solution provided in the above embodiment, where the dc system includes a first dc system and a second dc system, the first dc system is a bipolar two-terminal dc power transmission system of a first voltage class, the second dc system is a bipolar two-terminal dc power transmission system of a second voltage class, a first power transmission line of the first dc system and a second power transmission line of the second dc system are bridged at a predetermined crossover point, the first power transmission line and the second power transmission line are of the same polarity, and the crossover point is grounded; the method comprises the following steps:

501. and performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system.

502. Establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; and establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system.

503. And constructing a homopolar cross-over ground fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

504. And carrying out simulation operation on the same-polarity crossing ground fault model to obtain current simulation curves and trigger angle simulation curves of all converter stations in the same-polarity crossing ground fault model.

Specifically, the simulation operation generally includes an electromagnetic transient simulation software emtdc (electro magnetic transfer in DC system)/pscad (power Systems Computer Aided design) to build a same-polarity cross-over ground fault model, and then perform simulation.

505. And acquiring a fault network topological graph according to current simulation curves of all converter stations in the same-polarity cross-over earth fault model.

Specifically, the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first power transmission line and a second power transmission line and line resistance when the homopolar cross-over earth fault model is in a fault stage;

in practice, when dc systems of different levels cross each other in the same pole and cross the ground, the line with the crossover point is directly grounded, and no matter how the control system (converter station) controls, the current on the rectifying side of the fault line only flows into the ground, so that only one fault stage exists, and a fault network topological graph can be obtained according to the simulation operation result.

506. And establishing a fault boundary equation set for the fault network topological graph according to a preset rule.

507. Selecting current simulation curves of the converter stations in the fault network topological graph from current simulation curves of all converter stations in the homopolar cross-spanning ground fault model; and selecting the firing angle simulation curves of the converter stations in the fault network topological graph from the firing angle simulation curves of all converter stations in the homopolar cross-over earth fault model.

In particular, the converter station comprises a rectifying station.

508. And acquiring a first moment when the current is maximum in the fault stage in the current simulation curve of each converter station in the fault network topological graph.

509. And selecting trigger angle values of all first moments in a trigger angle simulation curve of a first converter station in the fault network topological graph as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the applause network topological graph.

Specifically, each converter station aims at one current simulation curve and one trigger angle simulation curve, so that a preset number of first moments exist in each converter station under the condition that current exists in each converter station all the time, the preset number is the number of the converter stations, and finally each converter station can obtain a preset number of trigger angle values aiming at a fault stage.

510. And according to an electromechanical transient simulation rule, grounding buses on the rectification side and the inversion side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance to generate a same-polarity cross-over grounding fault equivalent model.

511. And calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over earth fault at the fault stage according to the trigger angle value of the converter station in the fault network topological diagram, the fault boundary equation set and the preset rectification side equation set.

The embodiment of the invention provides a method for establishing a homopolar cross-over fault model between direct current systems, which comprises the following steps: performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; carrying out simulation operation on the homopolar crossing earth fault model and acquiring a fault network topological graph according to the simulation operation result of the homopolar crossing earth fault model; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage; establishing a fault boundary equation set for the fault network topological graph according to a preset rule; acquiring a trigger angle value of a converter station in a fault network topological graph according to a simulation operation result of a homopolar crossing earth fault model, wherein the converter station comprises a rectifier station; grounding buses on the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over grounding fault equivalent model; and calculating the value of the fault equivalent impedance of the equivalent model of the same polarity cross-over earth fault in the fault stage according to the trigger angle value of the converter station in the fault network topological diagram, the fault boundary equation set and the preset rectification side equation set. According to the technical scheme provided by the embodiment of the invention, firstly, a homopolar cross-over earth fault model of a direct current transmission system with different voltage levels is obtained by utilizing thevenin equivalence, then a network topological graph only having line resistance and a current converter in a fault stage and a current curve and a trigger angle curve of each converter station in the homopolar cross-over earth fault model are obtained according to a simulation result of the homopolar cross-over earth fault model, and then a boundary equation set related to the current and the voltage of the converter station can be obtained according to a preset rule according to the fault network topological graph, and the trigger angle of the converter station in the fault network topological graph is obtained according to the current curve and the trigger angle curve; finally, according to a trigger angle of a converter station in a network topological graph at a fault stage, a boundary equation set of each network topological graph and a preset rectifying side equation set, calculating a value of a fault impedance equivalence in the fault stage in a homopolar cross-over grounding fault equivalence model which can be used for electromechanical transient simulation by grounding a rectifying side bus and an inverting side bus of a bipolar line with a short-circuit fault in the homopolar cross-over grounding fault model in a homopolar cross-over grounding fault equivalence model according to an electromechanical transient simulation rule; and finally, combining known element parameters obtained from the homopolar cross-over ground fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ground fault equivalent model for analyzing homopolar cross-over ground faults between different direct current systems.

To more clearly show the method for establishing the homopolar crossing fault model between the dc systems according to the embodiment of the present invention, two dc systems corresponding to the homopolar crossing ground fault model shown in fig. 2 are taken as an example for explanation:

step one, single-port Thevenin equivalence is carried out on the rectifying side and the inverting side of the first direct current system and the second direct current system, so that Thevenin equivalent voltage sources (S1 and S2) and Thevenin equivalent impedances (Zeq1 and Zeq2) of all ports of the first direct current system are obtained; and thevenin equivalent voltage sources (S3 and S4) and thevenin equivalent impedances (Zeq3 and Zeq4) of the respective ports of the second direct current system; establishing an equivalent circuit 1 of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system; establishing an equivalent circuit 2 of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system; the same-polarity cross-over ground fault model diagram 2 is constructed according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system, wherein the first transmission line (positive polarity line) of the first direct current system is connected across to the crossover point f2 on the second transmission line (positive polarity line) of the second direct current system through a crossover point f1 and is grounded.

Step two, performing simulation operation on the model shown in the figure 2 by utilizing EMTDC/PSCAD to obtain current simulation curves and trigger angle simulation curves of all converter stations in the figure 2; acquiring a fault network topology according to current (Id11, Id21, Id31 and Id41) simulation curves of converter stations of the first transmission line and the second transmission line in the graph of FIG. 2;

specifically, as shown in fig. 6, the fault network topology map shows that the rectification-side direct current Id11 of the first transmission line (positive dc line) of the first dc system of the high voltage class flows to the crossover point f1 through the dc line resistor R11, f1 is shorted to the crossover point f2, f2 is grounded through the short-circuit transition resistor Rg, and the rectification-side direct current Id31 of the first transmission line (positive dc line) of the second dc system of the low voltage class flows to the fault crossover point f2 through the dc resistor R31.

Step three, establishing a fault boundary equation set aiming at the fault network topological graph according to the fault network topological graph shown in the figure 6 according to the kirchhoff current law and the kirchhoff voltage law,

the system of fault boundary equations is:

step four, determining the trigger angle of the converter station in the fault network topological graph applicable to the fault stage according to the current simulation curve and the trigger angle simulation curve corresponding to each converter station acquired in the step two;

for the converter stations in the fault network topology, selecting simulation curves Id11 and Id31 to find the maximum fault current time, which is recorded as T1n (n is 1, 3), respectively, and finding the trigger angle α corresponding to the T1n time in the trigger angle simulation curves of the rectifier station Rec11 of the first power transmission line and the rectifier station Rec31 of the second power transmission line_11,T1n、α_31,T1nWherein α_11,T1nFiring Angle for Rec11 failure in the first stage, α_31,T1nThe firing angle for a fault in the first stage for Rec 31.

Fifthly, according to the electromechanical transient simulation rule, the buses on the rectifying side and the inverting side of the first power transmission line and the second power transmission line in the same-polarity cross-over ground fault model shown in fig. 2 are grounded through fault equivalent impedances (Z11, Z21, Z31 and Z41) to establish the same-polarity cross-over ground fault equivalent model as shown in fig. 3.

Step six, because only the parameters of four equivalent impedances in the equivalent model of the homopolar cross-over ground fault obtained in the step five do not exist in practice, the values of the four equivalent impedances at different stages of faults need to be calculated;

specifically, because the model shown in fig. 3 is obtained from the equivalent values of the model shown in fig. 2, the bus voltage and the bus current value corresponding to four equivalent impedances of Z11, Z21, Z31 and Z41 in fig. 3 are the same as the bus voltage and the bus current corresponding to four converter stations of Rec11, Inv21, Rec31 and Inv41 in fig. 2; the rectifying side circuits where Rec11 and Rec31 are located both meet a preset rectifying side formula (1), and the current and voltage of Rec11 and Rec31 in a fault stage also respectively meet a fault boundary equation set (2);

in a fault stage, no current exists on the inversion sides of the first power transmission line and the second power transmission line, so that the values of Z21 and Z41 in the fault stage are infinite, an equation set related to the rectification sides where Rec11 and Rec31 are located is obtained according to a preset rectification side formula (1), parameters of a rectification side circuit where Rec11 is located and parameters of a rectification side circuit where Rec31 is located, and I exists in the equation sets corresponding to Rec11 and Rec31_dr、E_busr、μ_r、U_dr、

And I_busrSeven unknowns, so that the two corresponding equation sets of Rec11 and Rec31 have 14 unknowns in total, and the two equation sets are combined with the fault boundary equation set (2) to solve the converter bus voltages of the converter stations Rec11 and Rec31 at the time of the fault stage T1n (2)

And

) The converter bus currents of the converter stations Rec11 and Rec31 at the time of the fault phase T1n (r) ((r))

And

)；

then, the average voltage of the bus corresponding to Rec11 in the failure stage can be obtained

Average voltage of bus corresponding to fault stage Rec31

Average current of bus corresponding to fault stage Rec11

Average current of bus corresponding to fault stage Rec31

Finally, the equivalent impedance of the fault stage can be obtained

In summary, according to the method for establishing the homopolar cross-over fault model between the dc systems provided by the embodiments of the present invention, an equivalent model for analyzing the homopolar cross-over ground fault between different dc systems can be established.

Referring to fig. 7, an embodiment of the present invention further provides a device 01 for establishing a homopolar crossing fault model between dc systems, where the dc systems include a first dc system and a second dc system, the first dc system is a bipolar two-terminal dc power transmission system of a first voltage class, the second dc system is a bipolar two-terminal dc power transmission system of a second voltage class, a first power transmission line of the first dc system and a second power transmission line of the second dc system are bridged at a predetermined crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is grounded; the device includes: a model building module 71, a simulation module 72 and a processing module 73;

the model establishing module 71 is configured to perform single-port thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the simulation module 72 is configured to perform simulation operation on the homopolar cross-over ground fault model established by the model establishing module 71;

the model establishing module 71 is further configured to obtain a fault network topology map according to a simulation result of the simulation module 72 after the homopolar cross-over ground fault model is subjected to simulation operation; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage;

the processing module 73 is configured to establish a fault boundary equation set for the fault network topology map obtained by the model establishing module 71 according to a preset rule;

the processing module 73 is further configured to obtain, according to a result of simulation operation of the same-polarity-crossing ground fault model by the simulation module 72, a trigger angle value of the converter station in the fault network topology map obtained by the model establishing module 71;

the model establishing module 71 is further configured to ground buses on rectification sides and inversion sides of the first power transmission line and the second power transmission line in the same-polarity cross-over ground fault model through fault equivalent impedance according to an electromechanical transient simulation rule, and generate a same-polarity cross-over ground fault equivalent model;

the processing module 73 is further configured to calculate a value of the fault equivalent impedance of the equivalent model of the same-polarity cross-over ground fault at the fault stage according to the firing angle value of the converter station in the fault network topology map, the fault boundary equation set and the preset rectification side equation set, which is established by the model establishing module 71.

Optionally, the model building module 71 is specifically configured to: performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system to obtain Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system and Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

Optionally, the simulation module 72 is specifically configured to obtain current simulation curves of all converter stations in the same-polarity cross-over ground fault model after performing simulation operation on the same-polarity cross-over ground fault model established by the model establishing module 71; the model building module 71 is configured to obtain a fault network topology map according to the current simulation curves of all converter stations in the same-polarity cross-over ground fault model obtained by the simulation module 72.

Optionally, the simulation module 72 is configured to obtain firing angle simulation curves of all converter stations in the same-polarity cross-over ground fault model after performing simulation operation on the same-polarity cross-over ground fault model established by the model establishing module 71;

the processing module 73 is configured to select a current simulation curve of a converter station in the fault network topology map from current simulation curves of all converter stations in the same-polarity-crossing ground fault model acquired by the simulation module 72, and select a firing angle simulation curve of a converter station in the fault network topology map from firing angle simulation curves of all converter stations in the same-polarity-crossing ground fault model;

Optionally, the processing module 73 is specifically configured to: according to a trigger angle value, a fault boundary equation set and a preset rectification side equation set of a converter station in a fault network topological graph, calculating a voltage value and a current value of a bus corresponding to fault equivalent impedance of a homopolar cross-over ground fault equivalent model established by a model establishing module 71 at a fault stage;

The homopolar crossing fault model building device between the direct current systems provided by the embodiment of the invention comprises: the system comprises a model building module, a simulation module and a processing module; the model establishing module is used for performing single-port Thevenin equivalence on a rectification side and an inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over grounding fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system; the simulation module is used for carrying out simulation operation on the homopolar cross-over grounding fault model established by the model establishing module; the model building module is also used for acquiring a fault network topological graph according to a simulation result of the simulation module after the homopolar cross-over ground fault model is subjected to simulation operation; the fault network topological graph is a simplified model which comprises a converter station through which current passes in a first transmission line and a second transmission line and line resistance when a homopolar cross-over earth fault model is in a fault stage; the processing module is used for establishing a fault boundary equation set for the fault network topological graph acquired by the model establishing module according to a preset rule; the processing module is also used for acquiring the trigger angle value of the converter station in the fault network topological graph acquired by the model establishing module according to the simulation operation result of the simulation module on the homopolar crossing earth fault model; the model establishing module is also used for grounding buses at the rectification side and the inversion side of the first power transmission line and the second power transmission line in the same-polarity cross-over grounding fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over grounding fault equivalent model; the processing module is further used for calculating the value of the fault equivalent impedance of the same polarity cross-over grounding fault equivalent model established by the model establishing module according to the trigger angle value of the converter station in the fault network topological graph, the fault boundary equation set and the preset rectification side equation set in the fault network topological graph in the fault stage. Therefore, when the technical scheme provided by the embodiment of the invention is used for establishing an equivalent model for analyzing the homopolar crossing earth fault between different direct current systems, the homopolar crossing earth fault model of the direct current transmission system with different voltage levels can be obtained by utilizing thevenin equivalent firstly, then a network topological graph only having line resistance and a converter in a fault stage and current curves and trigger angle curves of all converter stations in the homopolar crossing earth fault model are obtained according to a simulation result of the homopolar crossing earth fault model, and then a boundary equation set related to the current and the voltage of the converter stations can be obtained according to a preset rule according to the fault network topological graph, and the trigger angles of the converter stations in the fault network topological graph are obtained according to the current curves and the trigger angle curves; finally, according to a trigger angle of a converter station in a network topological graph at a fault stage, a boundary equation set of each network topological graph and a preset rectifying side equation set, calculating a value of a fault impedance equivalence in the fault stage in a homopolar cross-over grounding fault equivalence model which can be used for electromechanical transient simulation by grounding a rectifying side bus and an inverting side bus of a bipolar line with a short-circuit fault in the homopolar cross-over grounding fault model in a homopolar cross-over grounding fault equivalence model according to an electromechanical transient simulation rule; and finally, combining known element parameters obtained from the homopolar cross-over ground fault model and the calculated value of the fault equivalent impedance to obtain a homopolar cross-over ground fault equivalent model for analyzing homopolar cross-over ground faults between different direct current systems.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied in hardware or in software instructions executed by a processor. Embodiments of the present invention also provide a storage medium, which may include a memory for storing computer software instructions for a method for building a homopolar cross-over fault model between dc systems, the computer software instructions including program code configured to perform the method for building a homopolar cross-over fault model between dc systems. Specifically, the software instructions may be composed of corresponding software modules, and the software modules may be stored in a Random Access Memory (RAM), a flash Memory, a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), a register, a hard disk, a removable hard disk, a compact disc Read Only Memory (CD-ROM), or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. Of course, the storage medium may also be integral to the processor. The processor and the storage medium may reside in an ASIC. Additionally, the ASIC may reside in a core network interface device. Of course, the processor and the storage medium may reside as discrete components in a core network interface device.

The embodiment of the invention also provides a computer program which can be directly loaded into the memory and contains software codes, and the computer program can realize the method for establishing the homopolar cross-over fault model between the direct current systems after being loaded and executed by the computer.

Those skilled in the art will recognize that, in one or more of the examples described above, the functions described in this invention may be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer.

The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for establishing homopolar cross-over fault model between DC systems is characterized in that,

the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is grounded; the method comprises the following steps:

carrying out simulation operation on the homopolar crossing earth fault model and acquiring a fault network topological graph according to the simulation operation result of the homopolar crossing earth fault model; the fault network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over earth fault model is in a fault stage;

acquiring a trigger angle value of a converter station in the fault network topological graph according to a simulation operation result of the homopolar crossing earth fault model;

grounding buses on rectification sides and inversion sides of the first power transmission line and the second power transmission line in the same-polarity cross-over ground fault model through fault equivalent impedance according to an electromechanical transient simulation rule to generate a same-polarity cross-over ground fault equivalent model;

calculating the value of the fault equivalent impedance of the equivalent model of the same-polarity cross-over ground fault at the fault stage according to the trigger angle value of the converter station in the fault network topological graph, the fault boundary equation set and a preset rectification side equation set;

obtaining the firing angle value of the converter station in the fault network topology according to the result of the simulation operation of the homopolar crossing earth fault model comprises:

acquiring a first moment when the current is maximum in the fault stage in a current simulation curve of each converter station in the fault network topological graph;

and selecting all the trigger angle values at the first moment in the trigger angle simulation curve of the first converter station in the fault network topology map as the trigger angle values of the first converter station, wherein the first converter station is any one converter station in the fault network topology map.

2. The method of claim 1, wherein the performing single-port Thevenin equivalence on the rectification side and the inversion side of the first DC system and the second DC system to obtain a homopolar cross-over ground fault model consisting of an equivalent circuit of the first DC system and an equivalent circuit of the second DC system comprises:

establishing an equivalent circuit of the first direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the first direct current system;

establishing an equivalent circuit of the second direct current system according to the Thevenin equivalent voltage source and Thevenin equivalent impedance of each port of the second direct current system;

and constructing the homopolar cross-over ground fault model according to the equivalent circuit of the first direct current system and the equivalent circuit of the second direct current system.

3. The method of claim 1, wherein said obtaining a fault network topology map from results of a simulation run of said homopolar crossover across ground fault model comprises:

obtaining current simulation curves of all converter stations in the same-polarity cross-over ground fault model after the same-polarity cross-over ground fault model is subjected to simulation operation;

and acquiring the fault network topological graph according to the current simulation curves of all converter stations in the same-polarity cross-over earth fault model.

4. The method according to claim 1, wherein the calculating the value of the fault equivalent impedance of the same-polarity cross-over ground fault equivalent model at the fault stage according to the firing angle values of the converter stations in the fault network topology map, the fault boundary equation set and a preset rectification side equation set comprises:

calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the homopolar cross-over ground fault equivalent model at the fault stage according to a trigger angle value of a converter station in the fault network topological graph, the fault boundary equation set and a preset rectification side equation set;

and calculating the value of the fault equivalent impedance of the same-polarity cross-over ground fault equivalent model in the fault stage according to the voltage value and the current value of the bus corresponding to the fault equivalent impedance of the same-polarity cross-over ground fault equivalent model in the fault stage.

5. A device for establishing homopolar cross-over fault model between DC systems is characterized in that,

the direct current system comprises a first direct current system and a second direct current system, the first direct current system is a bipolar two-end direct current power transmission system with a first voltage level, the second direct current system is a bipolar two-end direct current power transmission system with a second voltage level, a first power transmission line of the first direct current system and a second power transmission line of the second direct current system are bridged at a crossover point, the first power transmission line and the second power transmission line have the same polarity, and the crossover point is grounded; the device comprises: the system comprises a model building module, a simulation module and a processing module;

the model establishing module is used for performing single-port Thevenin equivalence on the rectification side and the inversion side of the first direct current system and the second direct current system so as to obtain a homopolar cross-over ground fault model formed by an equivalent circuit of the first direct current system and an equivalent circuit of the second direct current system;

the simulation module is used for carrying out simulation operation on the homopolar cross-over ground fault model established by the model establishing module;

the model establishing module is also used for acquiring a fault network topological graph according to a simulation result of the simulation module after the homopolar cross-over ground fault model is subjected to simulation operation; the fault network topological graph is a simplified model which comprises a converter station through which current passes in the first transmission line and the second transmission line and line resistance when the homopolar cross-over earth fault model is in a fault stage;

the processing module is further configured to obtain a trigger angle value of the converter station in the fault network topology map obtained by the model establishing module according to a result of simulation operation of the homopolar crossing earth fault model by the simulation module;

the model establishing module is further used for grounding buses on rectification sides and inversion sides of the first power transmission line and the second power transmission line in the same-polarity cross-over ground fault model through equivalent fault impedance according to an electromechanical transient simulation rule to generate an equivalent model of the same-polarity cross-over ground fault;

the processing module is further configured to calculate a value of the fault equivalent impedance of the same polarity cross-over ground fault equivalent model established by the model establishing module at the fault stage according to a trigger angle value of a converter station in the fault network topology, the fault boundary equation set and a preset rectification side equation set;

the simulation module is used for carrying out simulation operation on the homopolar crossing earth fault model established by the model establishing module and then acquiring the trigger angle simulation curves of all converter stations in the homopolar crossing earth fault model;

the processing module is used for selecting current simulation curves of the converter stations in the fault network topological graph from the current simulation curves of all the converter stations in the same-polarity cross-over ground fault model acquired by the simulation module, and selecting trigger angle simulation curves of the converter stations in the fault network topological graph from the trigger angle simulation curves of all the converter stations in the same-polarity cross-over ground fault model;

6. The apparatus of claim 5, wherein the model building module is specifically configured to:

7. The apparatus of claim 5,

the simulation module is specifically configured to obtain current simulation curves of all converter stations in the homopolar crossing ground fault model after performing simulation operation on the homopolar crossing ground fault model established by the model establishing module;

the model establishing module is used for acquiring the fault network topological graph according to the current simulation curves of all converter stations in the same polarity cross-over earth fault model acquired by the simulation module.

8. The apparatus of claim 5, wherein the processing module is specifically configured to:

calculating a voltage value and a current value of a bus corresponding to the fault equivalent impedance of the same polarity cross-over ground fault equivalent model established by the model establishing module at the fault stage according to a trigger angle value of a converter station in the fault network topological graph, the fault boundary equation set and a preset rectification side equation set;