Method for protecting flexible earthing system lines in power distribution networks and related equipment

Abstract

An embodiment of the present invention discloses a line protection method and related equipment for a flexible earthing system of a power distribution network, the method includes the steps of: when a ground fault occurs in a target power distribution network, a voltage source of a flexible earthing device of each line of the target power distribution network outputs a first compensation voltage, a zero-sequence impedance protection device starts to calculate the zero-sequence impedance of each line in real time, after outputting the first compensation voltage for a first output period, the voltage source of the flexible earthing device adjusts the output voltage to output a second compensation voltage, the zero-sequence impedance protection device of the lines calculates the zero-sequence impedance of each line in real time, the zero-sequence impedance protection device determines a faulted line that satisfies a zero-sequence impedance protection condition and a zero-sequence voltage protection condition based on the zero-sequence impedance, and disconnects the faulted line after a trip preset delay time of a line breaker to isolate the ground fault.

Description

[Technical field]

[0001] The present invention relates to the technical field of flexible earth protection of power distribution network, and more particularly to a line protection method and related equipment for a flexible earth system of a power distribution network. [Background technology]

[0002] The flexible grounding method of the neutral point of the power distribution network via a controllable voltage source has been widely applied to power distribution systems at home and abroad, making up for the shortcomings of the current arc-suppression reactor grounding system in that it cannot fully compensate for the fault current, and thoroughly eliminating the risk of secondary faults such as electric shock and forest fire caused by the residual voltage and residual current at the ground fault point. The flexible grounding method via a controllable voltage source can flexibly control the amplitude, phase and frequency of the fault point voltage, has a fast response speed, and can cooperate with the distribution automation circuit breaker FTU to quickly isolate the fault.

[0003] The flexible earthing method of the neutral point of the power distribution network through the voltage source and current source realizes the active, fast and safe treatment of the earth fault. However, the flexible earthing method changes the zero-sequence voltage of the neutral point of the system and the zero-sequence current of the line during the arc extinguishing, and the conventional technology of zero-sequence current protection and in-situ closing isolation by zero-sequence voltage cannot be applied during the flexible power injection. In response to the above problem, the present invention utilizes the principle that the zero-sequence impedance of the faulted line changes accordingly during the arc extinguishing adjustment by the flexible voltage source and current source, but the zero-sequence impedance of the non-faulted line does not change, to perform earth fault protection, and the method can also be applied to the earth fault selection device. Summary of the Invention [Problem to be solved by the invention]

[0004] A set of concepts introduced in a simplified form in the Summary are described in more detail in the Detailed Description section. This Summary is not intended to limit key or required features of the claimed subject matter, nor is it intended to define the scope of the claimed subject matter. [Means for solving the problem]

[0005] In order to provide a reliable line protection method for a flexible earthing system of a power distribution network, in a first aspect, the present invention provides a line protection method for a flexible earthing system of a power distribution network, the method comprising: When a ground fault occurs in a target power distribution network, a voltage source of a flexible grounding device of each line of the target power distribution network outputs a first compensation voltage, the first compensation voltage being opposite to a fault phase of a voltage corresponding to the ground fault; The zero-sequence impedance protection device detects a ground fault and calculates the zero-sequence impedance of each line in real time; After outputting the first compensation voltage for a first output period, the voltage source of the flexible grounding device adjusts the output voltage to continuously output a second compensation voltage for a second output period, and then ends a voltage source compensation mode; the zero-sequence impedance protection device calculates the zero-sequence impedance of each line in real time, the zero-sequence impedance including a maximum zero-sequence impedance and a minimum zero-sequence impedance; the zero-sequence impedance protection device determines a faulty line that satisfies a zero-sequence impedance protection condition and a zero-sequence voltage protection condition based on the zero-sequence impedance, and disconnects the faulty line after a trip preset delay time of a line breaker to isolate the ground fault; If there is no line that satisfies the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, the voltage source of the flexible earth device continues to output the first compensation voltage after a compensation preset delay time.

[0006] Optionally, the step of calculating the zero sequence impedance of each line of the zero sequence impedance protection device comprises: The zero-sequence impedance protection device includes calculating the zero-sequence impedance of each line according to a calculation formula of the zero-sequence impedance, where the calculation formula of the zero-sequence impedance is as follows:

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[0007] Optionally, the step of adjusting the output voltage of the voltage source of the flexible grounding device to output the second compensation voltage comprises: The voltage source of the flexible grounding device has an output voltage

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[0008] Optionally, the zero-sequence impedance protection condition is a zero-sequence impedance deviation ΔZ in the first period and the second period is greater than an impedance change protection constant Z zd or more, where the zero-sequence impedance deviation ΔZ is a difference between the maximum zero-sequence impedance and the minimum zero-sequence impedance, The above zero-phase voltage protection condition is that when the voltage source compensation mode is terminated, the zero-phase voltage setting value U 0z It is.

[0009] Optionally, the impedance change protection constant Z zd is set based on the sensitivity of the fault isolation, where the impedance change protection constant Z zd is the transient impedance Z that needs to be detected ABC is determined based on:

[0010] Optionally, the zero-phase voltage setting value U 0z is greater than 8V.

[0011] Optionally, the trip preset delay time is determined based on an installation position of the zero-sequence impedance protection device on the line, and a trip preset delay time of a zero-sequence impedance protection device close to a busbar is greater than a preset trip delay time of a zero-sequence impedance protection device away from the busbar, and the preset trip delay time difference is 0.1 seconds or more.

[0012] Optionally, the compensation preset delay time is greater than the trip preset delay time.

[0013] In a second aspect, the present invention can realize any of the flexible earth protection methods for a power distribution network as described in the first aspect of the claims, and further provides line protection-related equipment for a flexible earth system of a power distribution network, including a flexible earth device and a zero-phase impedance protection device.

[0014] Optionally, the zero-sequence impedance protection device includes: a voltage sensing unit used to convert a high-voltage voltage into signals such as low-voltage voltage, current, and frequency for easy collection and calculation; a current sensing unit used to convert a high-voltage zero-sequence current into signals such as low-voltage voltage, current, and frequency for easy collection and calculation; a control calculation unit used to calculate a zero-sequence impedance value of a line and a difference value between a maximum value and a minimum value of the zero-sequence impedance value, and determine whether to trip; and a trip unit used to control the closing or opening of a circuit breaker according to a command from the control calculation unit.

[0015] In a third aspect, the present invention further provides an electronic device comprising a memory, a processor and a computer program stored in said memory and executable by said processor, the processor, when executing the computer program stored in the memory, realising the steps of the method for flexible earth protection of a power distribution network of any one of the first aspects.

[0016] In a fourth aspect, the present invention further provides a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, realises any of the above-mentioned flexible earth protection methods for a power distribution network of the first aspect. Effect of the Invention

[0017] The implementation of the present invention has the following beneficial effects: The line protection method of the flexible earthing system of the power distribution network provided by the present application utilizes the characteristics that the zero-sequence impedance of the non-faulted line does not change with the output voltage of the flexible controllable voltage source, and the zero-sequence impedance of the faulted line changes with the output voltage of the flexible controllable voltage source, thereby ensuring the sensitivity, selectivity, reliability and rapid fault isolation of the line breaker protection, reducing the fault outage scope and improving the reliability of power supply. The method has relatively high sensitivity, selectivity and reliability for current active power and zero-sequence current protection, and can quickly isolate earth faults of 20 kΩ or less. It also solves the difficult problem that the feeder automated circuit breaker of the flexible grounding method of the power distribution network via a controllable voltage source has difficulty in performing protection based on features such as zero-sequence voltage and zero-sequence current, and does not need to judge the power direction, and provides an earth fault protection method for the distribution automated circuit breaker FTU. The earth fault protection method for the distribution automated circuit breaker provided by the present invention is advantageous for quickly removing permanent faults, improves the reliability of power supply, and assists in clean energy consumption and the construction of a new power distribution system. It also solves the difficult problem of selecting the earth fault line when extinguishing an earth fault in the grounding method using a flexible voltage source and current source, and can realize accurate earth fault line selection during the flexible power supply adjustment period. [Brief description of the drawings]

[0018] In the following, in order to more clearly explain the technical solutions in the embodiments of the present invention or the prior art, drawings that need to be used in the description of the embodiments or the prior art will be briefly introduced. Of course, the drawings described below are merely a part of the embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without any creative effort.

[0019] [Figure 1] 1 is a flowchart of a flexible ground protection method for a power distribution network provided by an embodiment of the present application. [Diagram 2] FIG. 1 is a schematic diagram of a simplified circuit for non-fault line impedance analysis of a neutral flexible grounding system provided by an embodiment of the present application. [Diagram 3]FIG. 2 is a schematic diagram of the electrical connection of the fault line of the neutral flexible grounding system provided by an embodiment of the present application. [Figure 4] FIG. 1 is a schematic diagram of a simplified circuit for fault line impedance analysis of a neutral flexible grounding system provided by an embodiment of the present application. [Diagram 5] FIG. 2 is a schematic diagram showing the arrangement of a power distribution network flexible ground zero-phase impedance protection device provided according to an embodiment of the present application along a line. [Figure 6] FIG. 2 is a structural schematic diagram of a line protection-related equipment of a flexible grounding system of a power distribution network provided by an embodiment of the present application; [Figure 7] 1 is a structural schematic diagram of a zero-phase impedance protection device provided by an embodiment of the present application; FIG. [Figure 8] FIG. 2 is a structural schematic diagram of a power distribution network flexible ground protection electronic device provided by an embodiment of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention, and obviously, the described embodiments are only some of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained based on the embodiments of the present invention without the creative labor of those skilled in the art are within the scope of protection of the present invention.

[0021] The terms "first", "second", "third" and "fourth" (if any) in the present specification and claims and the above drawings are used to distinguish between similar objects and are not necessarily used to describe a particular order or sequence. It is to be understood that the data used in this manner may be interchanged under appropriate circumstances so that the embodiments described herein may be performed in an order other than that shown or described herein. Furthermore, the terms "comprise" and "have" and any variations thereof are intended to cover a non-exclusive inclusion, such as a process, method, system, product or device that includes a series of steps or units is not necessarily limited to the steps or units specifically recited, and may include other steps or units that are not specifically recited or are inherent to such a process, method, product or device. Hereinafter, the technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application, and obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0022] As shown in FIG. 1, it is a flowchart of a flexible earth protection method for a power grid provided by an embodiment of the present application, specifically, Step S101, when a ground fault occurs in a target power distribution network, a voltage source of a flexible grounding device of each line of the target power distribution network outputs a first compensation voltage, the first compensation voltage being opposite to a fault phase of a voltage corresponding to the ground fault; A step S102 in which the zero-sequence impedance protection device detects a ground fault and calculates the zero-sequence impedance of each line in real time; Step S103: after outputting the first compensation voltage for a first output period, the voltage source of the flexible grounding device adjusts the output voltage to continuously output a second compensation voltage, and outputs the second compensation voltage for a second output period, and then ends the voltage source compensation mode; Step S104, in which the zero-sequence impedance protection device calculates the zero-sequence impedance of each line in real time, the zero-sequence impedance including a maximum zero-sequence impedance and a minimum zero-sequence impedance; Step S105: the zero-sequence impedance protection device determines a faulty line that satisfies a zero-sequence impedance protection condition and a zero-sequence voltage protection condition based on the zero-sequence impedance, and disconnects the faulty line after a trip preset delay time of a line breaker to isolate the ground fault; Step S106 includes, if there is no line that satisfies the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, the voltage source of the flexible earthing device continues to output the first compensation voltage after a compensation preset delay time.

[0023] Specifically, when it is monitored that a ground fault occurs in the target distribution network, the voltage source of the flexible earthing device in each line of the target distribution network outputs a first compensation voltage that is opposite to the fault phase of the voltage corresponding to the ground fault, thereby realizing full compensation of the line. In addition, when the zero-sequence impedance protection device detects a ground fault, it starts to calculate the zero-sequence impedance of the protection device attachment point in real time. After the first compensation voltage compensates for the first output period t, the voltage source of the flexible earthing device adjusts the output voltage to continuously output the second compensation voltage, and outputs for the second output period ts before terminating the voltage source compensation mode. The zero-sequence impedance protection device calculates the zero-sequence impedance of the first output period and the second output period in real time in each line, and the zero-sequence impedance includes a maximum zero-sequence impedance and a minimum zero-sequence impedance. If the zero-sequence impedance protection device detects a line that satisfies two conditions, the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, it is determined to be a faulty line, and the zero-sequence impedance protection device disconnects the faulty line after the trip preset delay time of the line breaker to isolate the ground fault. If there is no line that satisfies the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, the voltage source of the flexible earthing device continues to output the first compensation voltage after the compensation preset delay time, and continues full compensation.

[0024] In addition, the principle of using the above method to determine the fault line is as follows: Figure 2 is a schematic diagram of the non-fault line impedance analysis simplified circuit of the neutral flexible grounding system. As shown in Figure 2, the voltage output change of the flexible grounding device

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[0025] Figure 3 is a schematic diagram of the electrical connection of the fault line of the neutral flexible grounding system, and Figure 4 is a schematic diagram of the fault line impedance analysis simplified circuit of the neutral flexible grounding system. For the fault line, the line zero-sequence current is

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[0026] The impedance change protection constant Z zd Regarding the calculation, the error of the zero-phase impedance value Z0 detected by the zero-phase CT and PT of the zero-phase impedance protection device is 0.05Ω, and the zero-phase impedance of the fully compensated

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[0027] In summary, the zero-sequence impedance protection method for flexible earthing system of power distribution network provided by the present application utilizes the characteristics that the zero-sequence impedance of non-faulty lines does not change with the output voltage of the flexible controllable voltage source, and the zero-sequence impedance of the faulty line changes with the output voltage of the flexible controllable voltage source, to ensure the sensitivity, selectivity, reliability and rapid fault isolation of the line breaker protection, reduce the fault outage scope and improve the reliability of power supply. The method is superior to current active power and zero-sequence current protection methods, has relatively high sensitivity, selectivity and reliability, and can quickly isolate earth faults of 20 kΩ or less. It also solves the difficult problem that the feeder automated circuit breaker of the flexible grounding method of the power distribution network via a controllable voltage source has difficulty in performing protection based on features such as zero-sequence voltage and zero-sequence current, and does not need to determine the power direction, and provides an earth fault protection method for the distribution automated circuit breaker FTU. The earth fault protection method for the distribution automated circuit breaker provided by the present invention is advantageous for quickly removing permanent faults, improves the reliability of power supply, and supports clean energy consumption and the construction of a new power distribution system. It also solves the difficult problem of selecting the earth fault line when extinguishing an earth fault in the grounding method using a flexible voltage source and current source, and can realize accurate earth fault line selection during the flexible power supply adjustment period.

[0028] In some embodiments, the step of calculating the zero sequence impedance of each line of the zero sequence impedance protection device comprises: The zero-sequence impedance protection device includes calculating the zero-sequence impedance of each line according to a calculation formula for the zero-sequence impedance, where the calculation formula for the zero-sequence impedance is Equation (4):

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[0029] In some embodiments, the step of the voltage source of the flexible grounding device adjusting the output voltage to continuously output the second compensation voltage comprises: The voltage source of the flexible grounding device is an output voltage

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[0030] In some embodiments, the zero-sequence impedance protection condition is a condition in which the zero-sequence impedance deviation in the first period and the second period is greater than or equal to an impedance change protection constant Z zd or more, where the zero-sequence impedance deviation ΔZ is a difference between the maximum zero-sequence impedance and the minimum zero-sequence impedance, The above zero-phase voltage protection condition is that when the voltage source compensation mode is terminated, the zero-phase voltage setting value U 0z It is.

[0031] Specifically, if there exists a line that satisfies the zero-phase impedance protection condition and the zero-phase voltage protection condition in the zero-phase parameters of the line, the line that satisfies these two conditions is the faulty line. Here, the zero-phase impedance protection condition is a condition in which the zero-phase impedance deviation ΔZ is greater than or equal to the impedance change amount protection constant Z during the process from the occurrence of the fault to the output of the second compensation voltage (i.e., during the first period and the above-mentioned second period). zd The zero-phase impedance deviation ΔZ is the difference between the maximum zero-phase impedance and the minimum zero-phase impedance. The zero-phase voltage protection condition is that when the voltage source compensation mode is terminated, the zero-phase voltage setting value U obtained by measurement is 0z It is.

[0032] In some embodiments, the impedance change protection constant Z zd is set based on the sensitivity of fault isolation, where the impedance change protection constant is the transient impedance Z that needs to be detected. ABC is determined based on:

[0033] Specifically, Z zd The value of can be anywhere from 0.01 ohms to 1000 ohms.

[0034] In some embodiments, the zero-phase voltage setpoint U 0z is greater than 8V.

[0035] In some embodiments, the trip preset delay time is determined based on an installation position of the zero-sequence impedance protection device on the line, the trip preset delay time of the zero-sequence impedance protection device close to the bus is greater than the preset trip delay time of the zero-sequence impedance protection device away from the bus, and the preset trip delay time difference is 0.1 seconds or more.

[0036] Specifically, the trip preset delay time is determined based on the installation position on the line, the preset jump delay difference can be any value within the range of 0.1s to 10s, and the trip preset delay time of the zero-sequence impedance protection device close to the busbar is greater than the preset trip delay time of the zero-sequence impedance protection device away from the busbar.

[0037] In some embodiments, the compensation preset delay time is greater than the trip preset delay time.

[0038] As shown in FIG. 6 , the present invention can realize any of the flexible earth protection methods for a power distribution network described in the first aspect of the claims, and further provides a line protection-related equipment 200 of a flexible earth system for a power distribution network, including a flexible earth device 220 and a zero-phase impedance protection device 210.

[0039] As shown in FIG. 7, the zero-phase impedance protection device 210 includes a voltage sensing unit 2101 used to convert a high-voltage voltage into signals such as low-voltage voltage, current, and frequency for easier collection and calculation, a current sensing unit 2102 used to convert a high-voltage zero-phase current into signals such as low-voltage voltage, current, and frequency, a control calculation unit 2103 used to calculate the zero-phase impedance value of the line and the difference between the maximum and minimum values ​​of the zero-phase impedance value and determine whether to trip, and a trip unit 2104 used to control the closing or opening of the circuit breaker according to the command of the control calculation unit.

[0040] As shown in FIG. 8 , an embodiment of the present application further provides an electronic device 300 including a memory 310, a processor 320, and a computer program 311 stored in the memory 320 and executable by the processor, where the processor 320, when executing the computer program 311, realizes steps of the line protection method of the flexible earthing system of the power distribution network.

[0041] Since the electronic device introduced in this embodiment is an device used to implement the line protection device of the flexible grounding system of the power distribution network in the embodiment of the present application, those skilled in the art can know the specific embodiment of the electronic device of this embodiment and its various modifications based on the method introduced in the embodiment of the present application, therefore, this embodiment will not introduce in detail how the electronic device realizes the method in the embodiment of the present application, and any device used by those skilled in the art to implement the method in the embodiment of the present application falls within the scope of protection intended by the present application.

[0042] In a specific implementation process, the computer program 311 can realize any of the embodiments in the embodiments corresponding to FIG. 1 when executed by a processor.

[0043] In the above embodiments, the description of each embodiment is given with emphasis on its own, and for parts that are not described in detail in one embodiment, reference can be made to the descriptions of other embodiments.

[0044] It will be understood by those skilled in the art that the embodiments of the present application may be provided as a method, a system, or a computer program product. As such, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied in one or more computer usable storage mediums (including, but not limited to, magnetic disk memories, CD-ROMs, optical memories, etc.) having computer usable program code embodied therein.

[0045] The present application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and combinations of flows and / or blocks in the flowcharts and / or block diagrams, are realized by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing device to generate a machine, the instructions being executed by the processor of the computer or other programmable data processing device to generate an apparatus for implementing the functions specified in one or more flows of the flowcharts and / or one or more blocks of the block diagrams.

[0046] These computer program instructions may be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a particular manner, causing the instructions stored in the computer-readable memory to generate an article of manufacture including an instruction apparatus that implements the functions specified in one or more flows of the flowcharts and / or one or more blocks of the block diagrams.

[0047] These computer program instructions may be uploaded into a computer or other programmable data processing device which performs a series of operational steps to generate a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows of the flowcharts and / or one or more blocks of the block diagrams.

[0048] An embodiment of the present application further provides a computer program product including computer software instructions that, when executed on a processing device, cause the processing device to execute a flow of a line protection method for a flexible earthing system in a power distribution network in an embodiment corresponding to FIG.

[0049] A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed by a computer, the flow or function according to the embodiments of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another, for example, the computer instructions can be transmitted from one website site, computer, server, or data center to another website site, computer, server, or data center by wire (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, radio, microwave, etc.) methods. The computer-readable storage medium can be any available medium that can be stored in a computer, or a data storage device including a server, data center, etc. that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid state disks (SSDs)).

[0050] Those skilled in the art will clearly understand that for convenience and conciseness of description, the specific operating processes of the above-mentioned systems, devices and units can refer to the corresponding processes in the above-mentioned method embodiments, and the description will be omitted here.

[0051] In some embodiments provided in the present application, it should be understood that the disclosed system, device, and method may be realized in other forms. For example, the above-described device embodiments are merely exemplary, and the division of units is merely a division of logical functions, and in actual implementation, other division methods may be used, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted or not implemented. In other aspects, the shown or discussed mutual couplings or direct couplings or communication connections may be indirect couplings or communication connections via some interfaces, devices or units, which may be electrical, mechanical, or other forms.

[0052] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, i.e., they may be located in one place or distributed among multiple network units. According to actual needs, some or all of the units can be selected to achieve the objective of the solution of the present embodiment.

[0053] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, each unit may exist physically separately, or two or more units may be integrated into one unit. The integrated units may be realized in the form of hardware or software functional units.

[0054] When the integrated unit is realized in the form of a software functional unit and sold or used as an independent product, it can be stored in one computer-readable storage medium. Based on this understanding, the technical solution of the present application, essentially or a part that contributes to the prior art, or all or a part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium and includes some instructions for making a computer device (which may be a personal computer, a server, or a network device, etc.) execute all or a part of the steps of the method of each embodiment of the present application. In addition, the above-mentioned storage medium includes various media that can store program codes, such as a U disk, a portable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, an optical disk, etc.

[0055] What has been disclosed above is merely a preferred embodiment of the present invention, and it is obvious that the scope of the present invention cannot be limited thereby. Therefore, equivalent changes made based on the claims of the present invention still belong to the scope covered by the present invention.

[0056] (Additional Note) (Appendix 1) When a ground fault occurs in a target power distribution network, a voltage source of a flexible grounding device of each line of the target power distribution network outputs a first compensation voltage, the first compensation voltage being opposite to a fault phase of a voltage corresponding to the ground fault; The zero-sequence impedance protection device detects a ground fault and calculates the zero-sequence impedance of each line in real time; After outputting the first compensation voltage for a first output period, the voltage source of the flexible grounding device adjusts the output voltage to continuously output a second compensation voltage for a second output period, and then ends a voltage source compensation mode; the zero-sequence impedance protection device calculating the zero-sequence impedance of each line in real time, the zero-sequence impedance including a maximum zero-sequence impedance and a minimum zero-sequence impedance; the zero-sequence impedance protection device determines a faulty line that satisfies a zero-sequence impedance protection condition and a zero-sequence voltage protection condition based on the zero-sequence impedance, and disconnects the faulty line after a trip preset delay time of a line breaker to isolate the ground fault; If there is no line that satisfies the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, the voltage source of the flexible grounding device continues to output the first compensation voltage after a compensation preset delay time. A method for protecting a line in a flexible earthing system of a power distribution network, comprising:

[0057] (Appendix 2) The step of calculating the zero-sequence impedance of each line of the zero-sequence impedance protection device includes: The zero-sequence impedance protection device includes calculating the zero-sequence impedance of each line according to a calculation formula of the zero-sequence impedance, where the calculation formula of the zero-sequence impedance is as follows:

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[0058] (Appendix 3) The step of the voltage source of the flexible grounding device adjusting the output voltage to continuously output the second compensation voltage includes: The voltage source of the flexible grounding device has an output voltage

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[0059] (Appendix 4) The zero-phase impedance protection condition is that the zero-phase impedance deviation ΔZ in the first period and the second period is equal to or smaller than an impedance change amount protection constant Z zd or more, wherein the zero-sequence impedance deviation ΔZ is a difference between the maximum zero-sequence impedance and the minimum zero-sequence impedance, The zero-phase voltage protection condition is that when the voltage source compensation mode is terminated, the zero-phase voltage setting value U 0z That is, A line protection method for a flexible earthing system of a power distribution network as described in appendix 1.

[0060] (Appendix 5) The impedance change protection constant Z zd is set based on the sensitivity of fault isolation, where the impedance change protection constant Z zd is the transient impedance Z that needs to be detected ABC Determined based on A line protection method for a flexible earthing system of a power distribution network as described in Supplementary Note 4.

[0061] (Appendix 6) The zero-phase voltage setting value U 0z is greater than 8V, A line protection method for a flexible earthing system of a power distribution network as described in Supplementary Note 4.

[0062] (Appendix 7) The trip preset delay time is determined based on the installation position of the zero-sequence impedance protection device on the line, the trip preset delay time of the zero-sequence impedance protection device close to the busbar is greater than the preset trip delay time of the zero-sequence impedance protection device away from the busbar, and the preset trip delay time difference is 0.1 seconds or more. A line protection method for a flexible earthing system of a power distribution network as described in appendix 1.

[0063] (Appendix 8) the compensation preset delay time is greater than the trip preset delay time; A line protection method for a flexible earthing system of a power distribution network as described in appendix 1.

[0064] (Appendix 9) The flexible earth protection method for a power distribution network according to any one of appendices 1 to 8 can be realized, including a flexible earth device and a zero-phase impedance protection device; The present invention relates to a line protection-related device for a flexible earthing system of a power distribution network.

[0065] (Appendix 10) The zero-sequence impedance protection device includes: a voltage sensing unit used to convert a high-voltage voltage into signals such as low-voltage voltage, current, and frequency for easy collection and calculation; a current sensing unit used to convert a high-voltage zero-sequence current into signals such as low-voltage voltage, current, and frequency; a control calculation unit used to calculate a zero-sequence impedance value of a line and a difference value between a maximum value and a minimum value of the zero-sequence impedance value, and to determine whether to trip; and a trip unit used to control the closing or opening of a circuit breaker according to a command from the control calculation unit. 10. A line protection-related device for a flexible earthing system of a power distribution network as described in appendix 9.

Claims

1. When a ground fault occurs in a target power distribution network, a voltage source of a flexible grounding device of each line of the target power distribution network outputs a first compensation voltage, the first compensation voltage being opposite to a fault phase of a voltage corresponding to the ground fault; The zero-sequence impedance protection device detects a ground fault and calculates the zero-sequence impedance of each line in real time; After outputting the first compensation voltage for a first output period, the voltage source of the flexible grounding device adjusts the output voltage to continuously output a second compensation voltage for a second output period, and then ends a voltage source compensation mode; the zero-phase impedance protection device determines a faulty line that satisfies a zero-phase impedance protection condition and a zero-phase voltage protection condition based on the zero-phase impedance that changes in response to a change in the output of the flexible earthing device, and disconnects the faulty line after a trip preset delay time of a line breaker to isolate the ground fault; If there is no line that satisfies the zero-sequence impedance protection condition and the zero-sequence voltage protection condition, the voltage source of the flexible earthing device continues to output the first compensation voltage after a compensation preset delay time; Including, A method for protecting a line in a flexible earthing system of a power distribution network, comprising:

2. The step of calculating the zero-sequence impedance of each line of the zero-sequence impedance protection device includes: The zero-sequence impedance protection device includes calculating the zero-sequence impedance of each line according to a calculation formula of the zero-sequence impedance, where the calculation formula of the zero-sequence impedance is as follows: [0010] In the formula, Z ０ｉ is the zero-sequence impedance value of the i-th zero-sequence protection device attachment point, [0025] is the zero-sequence voltage of the i-th zero-sequence protection device attachment point, [0030] is the zero-sequence current of the i-th zero-sequence protection device attachment point, and Mod is a modulo function. The method for protecting a line of a flexible earthing system of a power distribution network according to claim 1.

3. The step of the voltage source of the flexible grounding device adjusting the output voltage to continuously output the second compensation voltage includes: The voltage source of the flexible grounding device has an output voltage [0045] The amplitude of U ｓ and / or adjusting the phase ψ to output a second compensation voltage, which may be a series of different voltages; Second Compensation Voltage [0050] The determination of the ground transient impedance Z ＡＢＣ , impedance change protection constant Z ｚｄ In relation to [006] is the faulted phase supply voltage, C is the faulted line capacitance to earth, [0070] is an absolute value, and the impedance change protection constant Z ｚｄ is determined by the following formula: The method for protecting a line of a flexible earthing system of a power distribution network according to claim 1. [0080]

4. The zero-sequence impedance protection device further includes a step of calculating in real time a zero-sequence impedance of each line, the zero-sequence impedance including a maximum zero-sequence impedance and a minimum zero-sequence impedance; The zero-phase impedance protection condition is that the zero-phase impedance deviation ΔZ in the first output period and the second output period is an impedance change amount protection constant Z ｚｄ or more, wherein the zero-sequence impedance deviation ΔZ is a difference between the maximum zero-sequence impedance and the minimum zero-sequence impedance, The zero-phase voltage protection condition is that the voltage value of the zero-phase voltage is equal to or smaller than the set value U of the zero-phase voltage obtained by measurement when the voltage source compensation mode is terminated. ０ｚ That is all. The method for protecting a line of a flexible earthing system of a power distribution network according to claim 1.

5. The impedance change protection constant Z ｚｄ is set based on the sensitivity of fault isolation, where the impedance change protection constant Z ｚｄ is the transient impedance Z that needs to be detected ＡＢＣ Determined based on The line protection method for a flexible earthing system of a power distribution network according to claim 4.

6. The zero-phase voltage setting value U ０ｚ is greater than 8V, The line protection method for a flexible earthing system of a power distribution network according to claim 4.

7. The trip preset delay time is determined based on the installation position of the zero-sequence impedance protection device on the line, the trip preset delay time of the zero-sequence impedance protection device close to the busbar is greater than the preset trip delay time of the zero-sequence impedance protection device away from the busbar, and the preset trip delay time difference is 0.1 seconds or more. The method for protecting a line of a flexible earthing system of a power distribution network according to claim 1.

8. the compensation preset delay time is greater than the trip preset delay time; The method for protecting a line of a flexible earthing system of a power distribution network according to claim 1.

9. The flexible earth protection method for a power distribution network according to any one of claims 1 to 8 can be realized, including a flexible earth device and a zero-phase impedance protection device; The present invention relates to a line protection-related device for a flexible earthing system of a power distribution network.

10. The zero-sequence impedance protection device includes: a voltage sensing unit used to convert a high-voltage voltage into signals such as low-voltage voltage, current, and frequency for easy collection and calculation; a current sensing unit used to convert a high-voltage zero-sequence current into signals such as low-voltage voltage, current, and frequency; a control calculation unit used to calculate a zero-sequence impedance value of a line and a difference value between a maximum value and a minimum value of the zero-sequence impedance value, and to determine whether to trip; and a trip unit used to control the closing or opening of a circuit breaker according to a command from the control calculation unit. The line protection related equipment of a flexible earthing system of a power distribution network according to claim 9.

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