A line differential protection method and system for longitudinal and transverse hybrid braking

Abstract

This invention discloses a line differential protection method and system with hybrid longitudinal and transverse braking. The method includes: correcting the phase differential current after a fault based on the voltage phasor sum and phase differential current calculation results before the fault, and calculating the differential current correction value for each phase; calculating the voltage phasor sum and correction value for each phase based on the rated voltage; and for any phase, determining the differential protection criterion for longitudinal and transverse braking based on the phase's differential current correction value and voltage phasor sum and correction value. Thus, by considering both the longitudinal and transverse dimensions of the line, a hybrid longitudinal and transverse braking differential protection system is constructed, significantly improving protection sensitivity while ensuring reliability.

Description

Technical Field

[0001] This invention relates to the field of electrical technology, and more specifically, to a line differential protection method and system with hybrid longitudinal and transverse braking. Background Technology

[0002] In existing AC systems, current differential protection is widely used as the main protection for line protection. Based on Kirchhoff's current law, current differential protection has zero differential current when there is no fault or an external fault, and becomes the fault current when there is an internal fault, exhibiting good sensitivity and reliability. However, due to the influence of the transmission line's capacitance to ground, the differential current is a capacitive current during normal operation. To improve the sensitivity of current differential protection, it is necessary to compensate for the capacitive current so that the differential current is zero when the line is fault-free. With the large-scale integration of new energy sources into new power systems, the fault current exhibits amplitude-limited characteristics due to the influence of control system strategies after new energy source faults. The fault characteristics on the new energy side are weakened, and the sensitivity of current differential protection based on fault current characteristics is significantly reduced. Furthermore, influenced by new energy control strategies, for AC lines transmitting from new energy sources, or scenarios where new energy is transmitted via flexible DC AC collection lines, AC line faults have a draining characteristic. During internal faults, the current phase on both sides of the line exhibits external fault characteristics, and current differential protection may fail to operate.

[0003] The aforementioned situation renders existing protection systems inadequate, and may even lead to incorrect protection actions, failing to promptly isolate faults and thus affecting system stability. Currently, large-scale centralized renewable energy transmission grids have experienced multiple instances of decreased sensitivity in AC convergence line relay protection devices. Summary of the Invention

[0004] According to the present invention, a method and system for differential protection of lines with hybrid longitudinal and transverse braking are provided to solve the problems that existing differential protection is inadequate, and may even result in incorrect protection operation and failure to promptly clear faults, thereby affecting system stability. Currently, large-scale renewable energy centralized transmission grids have experienced multiple technical problems of decreased sensitivity of AC collection line relay protection devices.

[0005] According to a first aspect of the present invention, a line differential protection method with cross-traffic hybrid braking is provided, comprising:

[0006] The differential current after the fault is corrected based on the calculation results of the voltage phasor and phase differential current before the fault, and the differential current correction value of each phase is calculated.

[0007] Calculate the voltage phasor and correction value for each phase based on the rated voltage;

[0008] For any phase, the differential protection criterion for longitudinal and transverse braking is determined based on the differential current correction value and the voltage phasor sum correction value of that phase.

[0009] Optionally, the phase differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault, including:

[0010] The differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault, and the correction value of the differential current for each phase is calculated:

[0011]

[0012] In the formula: This represents the differential current phasor value after a line fault. This is the sum of the voltage phasors on both sides of the line after the fault. The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault.

[0013] Optionally, based on the rated voltage, the voltage phasor and correction value for each phase are calculated, including:

[0014] The voltage phasors of each phase are corrected, and the voltage phasors and correction values ​​for each phase are calculated as follows:

[0015]

[0016] In the formula: U e This is the rated voltage.

[0017] Optionally, for any phase, the differential protection criterion for longitudinal and transverse braking is determined based on the differential current correction value and the voltage phasor sum correction value of that phase, including:

[0018] For any phase, use the smaller current value on both sides of the line. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase:

[0019]

[0020] In the formula: This is the differential current correction value; For voltage phasors and correction values; Y set Set the admittance value; These are the current values ​​on both sides of the line.

[0021] According to another aspect of the present invention, a line differential protection system with cross-traffic hybrid braking is also provided, comprising:

[0022] The differential current correction value calculation module is used to correct the phase differential current after the fault based on the voltage phasor and the calculation results of the phase differential current before the fault, and to calculate the differential current correction value for each phase.

[0023] The voltage phasor and correction value calculation module is used to calculate the voltage phasor and correction value for each phase based on the rated voltage.

[0024] The differential protection criterion module is used to determine the differential protection criterion for longitudinal and transverse braking of any phase based on the differential current correction value and the voltage phasor sum correction value of that phase.

[0025] Optionally, the module for calculating the differential current correction value includes:

[0026] The differential current correction calculation submodule corrects the phase differential current after the fault based on the pre-fault voltage phasor sum and the phase differential current calculation results, calculating the differential current correction value for each phase:

[0027]

[0028] In the formula: This refers to the phasor value of the line differential current; The sum of voltage phasors on both sides of the line; The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault.

[0029] Optionally, the module for calculating voltage phasors and correction values ​​includes:

[0030] The voltage phasor and correction value calculation submodule corrects the voltage phasor for each phase and calculates the voltage phasor and correction value for each phase:

[0031]

[0032] In the formula: U e This is the rated voltage.

[0033] Optionally, the differential protection criterion module includes:

[0034] The differential protection criterion submodule is used to determine the smaller current value on both sides of the line for any phase. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase:

[0035]

[0036] In the formula: This is the differential current correction value; For voltage phasors and correction values; Y set Set the admittance value; These are the current values ​​on both sides of the line.

[0037] Therefore, by constructing a hybrid differential protection system that combines longitudinal and transverse braking from both longitudinal and transverse dimensions, the system can significantly improve the sensitivity of the protection while ensuring reliability. This solves the problem that the performance of existing current differential protection is affected by the characteristics of power supply faults, and creates conditions for the large-scale consumption of clean energy. Attached Figure Description

[0038] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0039] Figure 1 This is a schematic flowchart of a line differential protection method with longitudinal and transverse hybrid braking as described in this embodiment.

[0040] Figure 2 This is a schematic diagram of the phase voltage phasor and correction described in this embodiment;

[0041] Figure 3 This is a schematic diagram of the high-proportion renewable energy access scenario described in this embodiment;

[0042] Figure 4 This is a schematic diagram of the line differential protection action results of the cross-sectional hybrid braking in the high proportion of new energy access scenario described in this embodiment.

[0043] Figure 5 This is a schematic diagram of the scenario where new energy is transmitted via flexible direct transmission as described in this embodiment;

[0044] Figure 6 This is a schematic diagram of the differential protection action result of the AC line longitudinal and transverse hybrid braking of the new energy transmitted via flexible DC islanding mode as described in this embodiment.

[0045] Figure 7 This is a schematic diagram of the installation of the controllable parallel reactor as described in this embodiment;

[0046] Figure 8 This is a schematic diagram of the differential protection operation result of the longitudinal and transverse mixed braking of the fault within the 100% energized zone of the controllable reactor described in this embodiment.

[0047] Figure 9 This is a schematic diagram of the differential protection operation result of the longitudinal and transverse hybrid braking of the fault in the 67% controllable reactor zone described in this embodiment.

[0048] Figure 10 This is a schematic diagram of the differential protection operation results of the line area with longitudinal and transverse mixed braking for faults, as described in this embodiment, with the installation of series compensation capacitors.

[0049] Figure 11 This is a system diagram of a conventional power supply access scenario as described in this embodiment;

[0050] Figure 12 This is a schematic diagram of the differential protection operation results of the mixed longitudinal and transverse braking in the fault zone described in this embodiment.

[0051] Figure 13 This is a schematic diagram of the differential protection operation results of the cross-sectional hybrid braking for external faults described in this embodiment.

[0052] Figure 14 This is a schematic diagram of a line differential protection system with hybrid longitudinal and transverse braking as described in this embodiment. Detailed Implementation

[0053] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0054] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0055] According to a first aspect of the present invention, a line differential protection method 100 with cross-traffic hybrid braking is provided, with reference to... Figure 1 As shown, the method 100 includes:

[0056] S101: Correct the phase differential current after the fault based on the calculation results of the voltage phasor and phase differential current before the fault, and calculate the differential current correction value for each phase.

[0057] S102: Calculate the voltage phasor and correction value for each phase based on the rated voltage;

[0058] S103: For any phase, determine the differential protection criterion for longitudinal and transverse braking of that phase based on the differential current correction value and the voltage phasor sum correction value of that phase.

[0059] Specifically, the method consists of the following steps.

[0060] (1) Construct differential protection for longitudinal and transverse hybrid braking.

[0061] Utilizing the smaller current on both sides of the line Longitudinal braking is achieved by utilizing the line capacitance current. The differential protection criteria for constituting lateral braking and longitudinal braking are as follows:

[0062]

[0063] In the formula: This is the differential current correction value; For voltage phasors and correction values; Y set Set the admittance value; These are the current values ​​on both sides of the line.

[0064] (2) Calculate the phase differential current correction value.

[0065] The differential current is corrected by using the voltage phasor sum and differential current before the fault, and the correction value of the differential current is calculated:

[0066]

[0067] In the formula: This refers to the phasor value of the line differential current; The sum of voltage phasors on both sides of the line; The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault.

[0068] (3) Calculate the voltage phasor and correction value.

[0069] Voltage phasor reference Figure 2 The voltage correction method in the text is used for correction, and the voltage phasor and correction value are:

[0070]

[0071] In the formula: U e This is the rated voltage.

[0072] (4) Differential protection for longitudinal and transverse hybrid braking is based on phase configuration criteria and does not require phase selection elements. If the differential protection criterion for phase-to-phase hybrid braking is met, then... Phase protection action.

[0073] The following scenarios were selected:

[0074] (1) High proportion of new energy access scenarios

[0075] In a high-proportion renewable energy integration scenario, offshore wind power is transmitted via submarine cable. An A / B phase-to-phase fault occurs at the cable's exit point F1. The system voltage level is 220kV. The system diagram is as follows. Figure 3As shown, the differential protection operation results of the longitudinal and transverse hybrid braking system are as follows: Figure 4 As shown, phase A enters the operating zone in 2.5ms, phase B enters the operating zone in 2.5ms, and phase C does not enter the operating zone, so the line protection operates reliably.

[0076] (2) New energy transmission via flexible direct transmission scenario

[0077] The scenario for transmitting new energy via flexible direct current is a scenario where new energy is transmitted in an islanded mode via flexible direct current, meaning the new energy access ratio is 100%, and an A / B phase-to-phase fault occurs on the AC outgoing line within the area. The system diagram is as follows. Figure 5 As shown, the differential protection operation results of the longitudinal and transverse hybrid braking system are as follows: Figure 6 As shown, phase A enters the operating zone at 1.67ms, phase B enters the operating zone at 2.5ms, and phase C does not enter the operating zone, indicating that the line protection operates reliably.

[0078] 3. Scenarios for connecting power electronic equipment

[0079] (1) AC lines with controllable parallel reactors installed

[0080] The circuit diagram for installing a controllable shunt reactor is shown below. Figure 7 As shown, when the controllable reactor is 100% engaged, if a single-phase ground fault AN occurs in the line area, the result of the line differential protection operation of the longitudinal and transverse hybrid braking system is as follows: Figure 8 As shown, phase A enters the operating zone in 2.5ms, while phases B and C do not, indicating that the line protection operates reliably.

[0081] When the controllable reactor is engaged at 67%, a single-phase ground fault AN occurs within the line area, and the operating result is as follows: Figure 9 As shown, phase A enters the action zone at 3.33ms.

[0082] (2) AC lines with series compensation capacitors installed

[0083] A simulation was performed on an AC transmission line with a series compensation capacitor installed. A single-phase ground fault (AN) occurred within the line area. The operational results are as follows: Figure 10 As shown, phase A enters the action zone at 3.33ms.

[0084] 4. Conventional power supply access scenarios

[0085] In a scenario where conventional power supply is used, both ends of the line are powered by conventional power sources, as shown in the system diagram below. Figure 11 As shown, the cases of faults within the line area and faults outside the line area are discussed separately.

[0086] Scene System Diagram

[0087] (1) Fault within the area

[0088] A single-phase ground fault occurred in the line area via an 800Ω transition resistor. The protection operation was as follows: Figure 12 As shown, phase A enters the operating region at 10.83ms, and the protection operates reliably.

[0089] (2) External fault

[0090] When a three-phase (A, B, C) fault occurs outside the designated area on the line, the protection system's operation is as follows: Figure 13 As shown, the protection for phases A, B, and C is reliable and does not malfunction.

[0091] Therefore, by constructing a hybrid differential protection system that combines longitudinal and transverse braking from both longitudinal and transverse dimensions, the system can significantly improve the sensitivity of the protection while ensuring reliability. This solves the problem that the performance of existing current differential protection is affected by the characteristics of power supply faults, and creates conditions for the large-scale consumption of clean energy.

[0092] Optionally, the phase differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault, and the differential current correction value for each phase is calculated, including:

[0093] The differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault, and the correction value of the differential current for each phase is calculated:

[0094]

[0095] In the formula: This represents the differential current phasor value after a line fault. This is the sum of the voltage phasors on both sides of the line after the fault. The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault.

[0096] Optionally, based on the rated voltage, the voltage phasor and correction value for each phase are calculated, including:

[0097] The voltage phasors of each phase are corrected, and the voltage phasors and correction values ​​for each phase are calculated as follows:

[0098]

[0099] In the formula: U e This is the rated voltage.

[0100] Optionally, for any phase, the differential protection criterion for longitudinal and transverse braking is determined based on the differential current correction value and the voltage phasor sum correction value of that phase, including:

[0101] For any phase, use the smaller current value on both sides of the line. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase:

[0102]

[0103] In the formula: This is the differential current correction value; For voltage phasors and correction values; Y set Set the admittance value; These are the current values ​​on both sides of the line.

[0104] Therefore, by considering both the longitudinal current and the transverse line dimensions, a hybrid longitudinal and transverse braking differential protection system is constructed. This system not only ensures reliability but also significantly improves the sensitivity of the protection, solving the problem that the performance of existing current differential protection is affected by power supply fault characteristics, and creating conditions for the large-scale consumption of clean energy.

[0105] According to another aspect of the invention, a line differential protection system 1400 with cross-traffic hybrid braking is also provided, referenced to... Figure 14 As shown, the system 1400 includes:

[0106] The differential current correction value calculation module 1410 is used to correct the phase differential current after the fault based on the calculation results of the voltage phasor and phase differential current before the fault, and to calculate the differential current correction value for each phase.

[0107] The voltage phasor and correction value calculation module 1420 is used to calculate the voltage phasor and correction value for each phase based on the rated voltage.

[0108] The differential protection criterion module 1430 is used to determine the differential protection criterion for longitudinal and transverse braking of any phase based on the differential current correction value and the voltage phasor sum correction value of that phase.

[0109] Optionally, the module for calculating the differential current correction value includes:

[0110] The differential current correction calculation submodule corrects the phase differential current after the fault based on the pre-fault voltage phasor sum and the phase differential current calculation results, calculating the differential current correction value for each phase:

[0111]

[0112] In the formula: This refers to the phasor value of the line differential current; The sum of voltage phasors on both sides of the line; The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault.

[0113] Optionally, the module for calculating voltage phasors and correction values ​​includes:

[0114] The voltage phasor and correction value calculation submodule corrects the voltage phasor for each phase and calculates the voltage phasor and correction value for each phase:

[0115]

[0116] In the formula: U e This is the rated voltage.

[0117] Optionally, the differential protection criterion module includes:

[0118] The differential protection criterion submodule is used to determine the smaller current value on both sides of the line for any phase. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase:

[0119]

[0120] In the formula: This is the differential current correction value; For voltage phasors and correction values; Y set Set the admittance value; These are the current values ​​on both sides of the line.

[0121] The line differential protection system 1400 with hybrid longitudinal and transverse braking according to an embodiment of the present invention corresponds to the line differential protection method 100 with hybrid longitudinal and transverse braking according to another embodiment of the present invention, and will not be described again here.

[0122] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0123] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0124] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0125] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0126] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0127] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A differential protection method for lines with hybrid longitudinal and transverse braking, characterized in that, include: The differential current after the fault is corrected based on the calculation results of the voltage phasor and phase differential current before the fault, and the differential current correction value of each phase is calculated. Calculate the voltage phasor and correction value for each phase based on the rated voltage; For any phase, the differential protection criterion for longitudinal and transverse braking is determined based on the differential current correction value and the voltage phasor sum correction value of that phase. The phase differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault. The correction value of the differential current for each phase is calculated, including: The differential current after the fault is corrected based on the voltage phasor sum and the calculation results of the phase differential current before the fault, and the correction value of the differential current for each phase is calculated: In the formula: This represents the differential current phasor value after a line fault. This is the sum of the voltage phasors on both sides of the line after the fault. The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault. For any phase, the differential protection criteria for longitudinal and transverse braking of that phase are determined based on the differential current correction value and the voltage phasor sum correction value of that phase, including: For any phase, use the smaller current value on both sides of the line. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase: In the formula: This is the differential current correction value; For voltage phasors and correction values; Set the admittance value; ; , These are the current values ​​on both sides of the line.

2. The method according to claim 1, characterized in that, Based on the rated voltage, calculate the voltage phasor and correction value for each phase, including: The voltage phasors of each phase are corrected, and the voltage phasors and correction values ​​for each phase are calculated as follows: In the formula: This is the rated voltage.

3. A line differential protection system with hybrid longitudinal and transverse braking, characterized in that, include: The differential current correction value calculation module is used to correct the phase differential current after the fault based on the voltage phasor and the calculation results of the phase differential current before the fault, and to calculate the differential current correction value for each phase. The voltage phasor and correction value calculation module is used to calculate the voltage phasor and correction value for each phase based on the rated voltage. The differential protection criterion module is used to determine the differential protection criterion for longitudinal and transverse braking of any phase based on the differential current correction value and the voltage phasor sum correction value of that phase. The module for calculating differential current correction values ​​includes: The differential current correction calculation submodule corrects the phase differential current after the fault based on the pre-fault voltage phasor sum and the phase differential current calculation results, calculating the differential current correction value for each phase: In the formula: This represents the differential current phasor value after a line fault. This is the sum of the voltage phasors on both sides of the line after the fault. The differential current phasor value of the line before the fault; This is the sum of the voltage phasors on both sides of the line before the fault. The differential protection criterion module includes: The differential protection criterion submodule is used to determine the smaller value of the current on both sides of the line for any phase. Longitudinal braking is achieved by utilizing the line capacitance current. To achieve lateral braking, the differential protection criterion for longitudinal and lateral braking of a phase is determined based on the differential current correction value and the voltage phasor sum correction value of that phase: In the formula: This is the differential current correction value; For voltage phasors and correction values; Set the admittance value; ; , These are the current values ​​on both sides of the line.

4. The system according to claim 3, characterized in that, The module for calculating voltage phasors and correction values ​​includes: The voltage phasor and correction value calculation submodule corrects the voltage phasor for each phase, calculating the voltage phasor and correction value for each phase: In the formula: This is the rated voltage.

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