A method for ground fault protection of a flexible interconnected power distribution grid and related apparatus

Abstract

The present application relates to the technical field of power distribution network, and more particularly to a grounding fault protection method for flexible interconnected power distribution network and related device, the method comprising: putting in a fault feature enhancement module; obtaining and determining the zero sequence current direction of each outgoing line according to the zero sequence voltage of the bus and the zero sequence current of each outgoing line; and determining the target outgoing line; when there is only one target outgoing line, and the amplitude of the zero sequence current of the target outgoing line is greater than the preset current threshold, cutting off the target outgoing line; when there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero sequence current of the target outgoing line is not greater than the current threshold, using a preset round cutting strategy to round cut all outgoing lines in turn until the fault object is determined; when there is no target outgoing line, or when the fault object is a non-outgoing line object, locking the tripping mechanism of all outgoing lines, solving the technical problem of poor reliability of the existing grounding fault protection method for flexible interconnected power distribution network.

Description

Technical Field

[0001] This invention relates to the field of power distribution network technology, and in particular to a ground fault protection method and related apparatus for a flexible interconnected power distribution network. Background Technology

[0002] In the field of power distribution networks, non-isolated flexible interconnection equipment has been widely adopted due to its structural advantage of eliminating the need for power frequency isolation transformers, effectively improving the operating efficiency and power density of power distribution systems. However, this lightweight structure of non-isolated flexible interconnection equipment, by eliminating the power frequency isolation transformer, creates electrical connectivity at the zero-sequence level between interconnected AC power distribution systems when used to construct a flexible interconnected power distribution network. When a single-phase ground fault occurs on either side of the power distribution system, the resulting zero-sequence voltage and current will be conducted across regions to the normally operating healthy side system via the flexible interconnection equipment. This cross-side transmission of zero-sequence components further disrupts the operating logic of the original grounding protection system of the AC power distribution system, triggering multiple protection anomalies. Specifically, in low-current grounding systems, the direction of the zero-sequence current is distorted, easily causing fault location devices to misjudge the fault; in low-resistance grounding systems, the transmitted zero-sequence current may directly exceed the protection setting value, thereby inducing unwarranted tripping of healthy lines and affecting the stability of the power supply of the power distribution network.

[0003] To address the protection disturbance problem caused by the propagation of zero-sequence components, existing technologies propose two types of solutions. The first type primarily optimizes the flexible interconnection equipment in the system. Specifically, this involves adjusting the converter modulation logic or switching full-bridge submodules to generate a voltage component opposite to the propagated zero-sequence voltage, thereby canceling or suppressing the propagated zero-sequence component. The second type employs a protection system based on the differential principle. Protection units are installed at key nodes on both sides of the interconnection area, and current data from both sides are synchronized via a high-speed communication channel. By comparing the phase and amplitude differences of the currents on both sides, the fault area is determined, thus achieving selective tripping.

[0004] However, both existing solutions have shortcomings and are difficult to adapt to the practical needs of large-scale distribution network applications. For the first type of solution, its effectiveness is limited by the control margin of the flexible interconnection equipment itself, as it relies on the SOP (Standard Operating Procedure) zero-sequence suppression strategy. When a single-phase ground fault occurs, the voltage of the non-faulty phase may rise to the line voltage. At this point, the basic modulation ratio required by the flexible interconnection equipment to maintain stable operation is close to or has reached saturation, making it difficult to provide additional voltage capacity for zero-sequence component suppression, resulting in poor suppression or even complete failure. For the second type of solution, the overall architecture is complex, construction and maintenance costs are high, and it is highly dependent on the stability of the communication channel, requiring extremely high reliability. In large-scale distribution network applications or when the communication system fails, the reliability of this solution will face severe challenges.

[0005] Therefore, existing ground fault protection methods for flexible interconnected distribution networks suffer from poor reliability. Summary of the Invention

[0006] This invention provides a ground fault protection method and related apparatus for flexible interconnected distribution networks, which solves the technical problem of poor reliability in existing ground fault protection methods for flexible interconnected distribution networks.

[0007] This invention provides a ground fault protection method for a flexible interconnected distribution network. When a single-phase ground fault is detected, the method includes:

[0008] A fault feature enhancement module is deployed, which is used to change the zero-sequence impedance characteristics;

[0009] The direction of the zero-sequence current of each outgoing line is determined based on the zero-sequence voltage of the busbar and the zero-sequence current of each outgoing line; and the outgoing line whose zero-sequence current direction is from the outgoing line to the busbar is taken as the target outgoing line.

[0010] When there is only one target output line, and the amplitude of the zero-sequence current of the target output line is greater than a preset current threshold, the target output line is disconnected.

[0011] When there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, a preset round-cutting strategy is adopted to sequentially cut all the outgoing lines until the faulty object is determined.

[0012] When the target outgoing line does not exist, or when the faulty object is a non-outgoing line object, the tripping mechanism of all the outgoing lines is locked.

[0013] Optionally, the step of sequentially switching all outgoing lines using a preset switching strategy until a faulty object is identified includes:

[0014] S1. Following the preset cutting sequence, cut one of the outgoing lines in sequence;

[0015] S2. Based on the time after the cut-off, after a preset time, obtain and determine whether the zero-sequence voltage of the bus is less than the preset voltage threshold. If yes, determine that the faulty object is an outgoing line and the rotational cutting ends; otherwise, jump to execute S3.

[0016] S3. Determine if the outgoing line is at the end of the sequence. If yes, determine if the faulty object is a non-outgoing object. If not, jump to execute S1 to S2.

[0017] Optionally, determining the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line includes:

[0018] The instantaneous value of the zero-sequence current of each outgoing line is determined based on the zero-sequence current of each outgoing line, and the instantaneous value of the zero-sequence voltage of the bus is determined based on the zero-sequence voltage of the bus.

[0019] The zero-sequence current direction coefficient is calculated based on the instantaneous value of the zero-sequence current of each outgoing line and the instantaneous value of the zero-sequence voltage of the bus.

[0020] The direction of the zero-sequence current in each outgoing line is determined by comparing the zero-sequence current direction coefficient with a preset threshold.

[0021] Optionally, determining the zero-sequence current direction of each outgoing line based on the comparison result of the zero-sequence current direction coefficient and a preset threshold includes:

[0022] Determine whether the zero-sequence current direction coefficient is less than a preset threshold. If it is, determine that the direction of the zero-sequence current is from the outgoing line to the busbar; otherwise, determine that the direction of the zero-sequence current is from the busbar to the outgoing line.

[0023] Optionally, the fault feature enhancement module is connected in parallel across the two ends of the grounding element of the AC power distribution system, and the grounding element is connected between the neutral point of the AC power distribution system and the ground.

[0024] Optionally, the fault feature enhancement module includes a resistor assembly and a control switch connected to the resistor assembly;

[0025] The control switch is used to engage or disengage the resistor assembly.

[0026] In another aspect, the present invention provides a ground fault protection device for a flexible interconnected distribution network, applicable to the AC distribution system on any side of the flexible interconnected distribution network, the device comprising:

[0027] The activation unit is used to activate the fault feature enhancement module when a single-phase ground fault is detected. The fault feature enhancement module is used to change the zero-sequence impedance characteristics.

[0028] The determining unit is used to acquire and determine the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line; and to designate the outgoing line whose zero-sequence current direction is from the outgoing line to the bus as the target outgoing line.

[0029] The first cut-off unit is used to cut off the target outgoing line when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than a preset current threshold.

[0030] The second cut-off unit is used to sequentially cut off all the outgoing lines in turn using a preset round-cutting strategy when there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, until the fault object is determined.

[0031] The interlocking unit is used to interlock the tripping mechanism of all outgoing lines when the target outgoing line does not exist, or when the faulty object is a non-outgoing line object.

[0032] In another aspect, the present invention provides a flexible interconnected power distribution network, comprising: a first AC power distribution system, a second AC power distribution system, and flexible interconnection equipment;

[0033] The first AC power distribution system is connected to the flexible interconnection device, and is also connected to the second AC power distribution system through the flexible interconnection device;

[0034] The neutral point of the first AC power distribution system is connected to one end of the first grounding element, and the other end of the first grounding element is grounded.

[0035] The neutral point of the second AC power distribution system is connected to one end of the second grounding element, and the other end of the second grounding element is grounded.

[0036] A first fault feature enhancement module is connected in parallel to both ends of the first grounding element; a second fault feature enhancement module is connected in parallel to both ends of the second grounding element.

[0037] The first fault feature enhancement module is connected to the first control unit; the second fault feature enhancement module is connected to the second control unit.

[0038] The first control unit is used to perform the method described above;

[0039] The second control unit is used to perform the method described above.

[0040] In another aspect, the present invention provides an electronic device, including a processor and a memory;

[0041] The memory is used to store program code and transmit the program code to the processor;

[0042] The processor is used to execute the method described above according to the instructions in the program code.

[0043] In another aspect, the present invention provides a computer-readable storage medium for storing program code for performing the method described above.

[0044] As can be seen from the above technical solutions, the present invention has the following advantages:

[0045] This invention provides a ground fault protection method for a flexible interconnected distribution network, applicable to the AC distribution system on any side of the flexible interconnected distribution network. When a single-phase ground fault is detected, the method includes: activating a fault feature enhancement module, which is used to change the zero-sequence impedance characteristics; acquiring and determining the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line; and designating the outgoing line whose zero-sequence current direction is from the outgoing line to the bus as the target outgoing line; when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than a preset current threshold, disconnecting the target outgoing line; when there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, sequentially disconnecting all outgoing lines using a preset rotation strategy until a fault object is determined; when there is no target outgoing line, or when the fault object is a non-outgoing line object, blocking the tripping mechanism of all outgoing lines.

[0046] In this invention, when a single-phase ground fault occurs in a flexible interconnected distribution network, the zero-sequence component generated by the single-phase ground fault is conducted to the AC distribution systems on both sides based on the flexible interconnection equipment in the flexible interconnected distribution network, so that both AC distribution systems on both sides detect the single-phase ground fault. For any AC distribution system, when a single-phase ground fault is detected, a fault feature enhancement module is activated to change its own zero-sequence impedance characteristics and enhance the fault features, thereby providing basic support for the discrimination of the zero-sequence current direction of each outgoing line; then, by acquiring and based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line, the zero-sequence current direction of each outgoing line is determined, realizing the determination of the zero-sequence current direction of each outgoing line, and the outgoing line whose zero-sequence current direction is from the outgoing line to the bus is taken as the target outgoing line, providing technical support for the discrimination of the target outgoing line. Then, this invention determines different protection strategies based on the number of target outgoing lines and the zero-sequence current amplitude. Specifically, when there is only one target outgoing line, and When the amplitude of the zero-sequence current of the target outgoing line is greater than a preset current threshold, the target outgoing line is determined to be a faulty line and the target outgoing line is disconnected. When there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, it indicates that the fault object is not clear. Therefore, a preset round-trip strategy is adopted to sequentially disconnect all the outgoing lines until the fault object is determined, thereby reliably locating and isolating the fault. When there is no target outgoing line, or when the fault object is a non-outgoing line object, to avoid the fault not appearing on the outgoing line, the tripping mechanism of all the outgoing lines is locked to prevent false tripping caused by a fault in the AC distribution system on the other side.

[0047] Therefore, the ground fault protection method for flexible interconnected distribution networks provided by this invention solves the technical problem of poor reliability of existing ground fault protection methods for flexible interconnected distribution networks. Moreover, this invention does not require modification of the original control strategy of the flexible interconnected equipment, nor does it require the establishment of a high-speed communication channel between the protection devices on both sides of the flexible interconnected equipment, thus further improving reliability and economy. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 A schematic diagram of a circuit topology for a flexible interconnected distribution network provided in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of the control subunit provided in an embodiment of the present invention;

[0051] Figure 3 This is one of the flowcharts illustrating a ground fault protection method for a flexible interconnected distribution network provided in an embodiment of the present invention;

[0052] Figure 4 A second schematic flowchart of a ground fault protection method for a flexible interconnected distribution network provided in an embodiment of the present invention;

[0053] Figure 5 The third schematic flowchart of a ground fault protection method for a flexible interconnected distribution network provided in this embodiment of the invention;

[0054] Figure 6 A schematic flowchart of a ground fault protection method for a flexible interconnected distribution network is provided as an application example of the present invention.

[0055] Figure 7 A structural block diagram of a ground fault protection device for a flexible interconnected distribution network provided in an embodiment of the present invention;

[0056] Figure 8 This is a structural block diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0057] This invention provides a ground fault protection method and related apparatus for flexible interconnected distribution networks, which solves the technical problem of poor reliability in existing ground fault protection methods for flexible interconnected distribution networks.

[0058] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0059] To facilitate a clear understanding of the ground fault protection method for a flexible interconnected distribution network provided by the embodiments of the present invention, the following will first describe a flexible interconnected distribution network involved in the embodiments of the present invention.

[0060] In one embodiment, see Figure 1 , Figure 1 The circuit topology of a flexible interconnected distribution network provided by an embodiment of the present invention is shown.

[0061] An embodiment of the present invention provides a flexible interconnected power distribution network, comprising: a first AC power distribution system 1, a second AC power distribution system 2, and a flexible interconnection device 3;

[0062] The first AC power distribution system 1 is connected to the flexible interconnection device 3, and is also connected to the second AC power distribution system 2 through the flexible interconnection device 3;

[0063] The neutral point of the first AC power distribution system 1 is connected to one end of the first grounding element, and the other end of the first grounding element is grounded.

[0064] The neutral point of the second AC power distribution system 2 is connected to one end of the second grounding element, and the other end of the second grounding element is grounded.

[0065] The first fault feature enhancement module 11 is connected in parallel to both ends of the first grounding element; the second fault feature enhancement module 21 is connected in parallel to both ends of the second grounding element.

[0066] The first fault feature enhancement module 11 is connected to the first control unit 12; the second fault feature enhancement module 21 is connected to the second control unit 22;

[0067] The first control unit 12 is used to execute a ground fault protection method for a flexible interconnected distribution network provided in any of the following embodiments;

[0068] The second control unit 22 is used to perform a ground fault protection method for a flexible interconnected distribution network provided in any of the following embodiments.

[0069] It should be noted that both the first AC power distribution system 1 and the second AC power distribution system 2 include transformers. Each transformer is equipped with a busbar, outgoing lines, and a neutral point. The neutral point refers to the neutral point where the AC busbar provides a zero-sequence path, such as the neutral point of a distribution transformer, a connecting transformer, or a dedicated grounding resistor cabinet.

[0070] like Figure 1 As shown, the output line of the transformer in the first AC power distribution system 1 is connected to the flexible interconnection device 3, and the output line of the transformer in the second AC power distribution system 2 is connected to the flexible interconnection device 3. Based on this, the first AC power distribution system 1 and the second AC power distribution system 2 are interconnected.

[0071] In the first AC power distribution system 1, the neutral point of the transformer is connected to the first grounding element and grounded through the first grounding element; in the second AC power distribution system 2, the neutral point of the transformer is connected to the second grounding element and grounded through the second grounding element.

[0072] The first fault characteristic enhancement module 11 is connected in parallel with the first grounding element. The first control unit 12 is connected to the first fault characteristic enhancement module 11 and is used to control the activation and deactivation of the first fault characteristic enhancement module 11. When the first control unit 12 detects a single-phase ground fault, it activates the first fault characteristic enhancement module 11, forming a path between the first fault characteristic enhancement module 11, the neutral point, and the ground, thereby changing the zero-sequence impedance characteristics and zero-sequence current distribution of the first AC power distribution system 1 and enhancing the fault characteristics.

[0073] The second fault characteristic enhancement module 21 is connected in parallel with the second grounding element. The second control unit 22 is connected to the second fault characteristic enhancement module 21 and is used to control the activation and deactivation of the second fault characteristic enhancement module 21. When the second control unit 22 detects a single-phase ground fault, it activates the second fault characteristic enhancement module 21, forming a path between the second fault characteristic enhancement module 21, the neutral point, and the ground, thereby changing the zero-sequence impedance characteristics and zero-sequence current distribution of the second AC power distribution system 2 and enhancing the fault characteristics.

[0074] Due to the interconnection characteristics of the first AC power distribution system 1 and the second AC power distribution system 2, when a single-phase ground fault occurs in either AC power distribution system, the zero-sequence component generated by the fault will be transmitted to the AC power distribution system on the non-fault side through the flexible interconnection device 3. Since the transmission speed of the zero-sequence component is very fast, the control units in the two AC power distribution systems can detect the single-phase ground fault almost simultaneously, thereby synchronously activating the corresponding fault feature enhancement module and performing accurate fault location according to the method provided in the following method embodiment, reducing the risk of false activation of fault protection.

[0075] Specifically, the working principle of the flexible interconnected distribution network provided in this embodiment is as follows:

[0076] During normal operation of the flexible interconnected distribution network, the first control unit 12 monitors the zero-sequence voltage of the busbar of the first AC distribution system 1 in real time. The second control unit 22 monitors the zero-sequence voltage of the busbar of the second AC power distribution system 2 in real time. When either control unit detects the zero-sequence voltage of the busbar... The effective value exceeds the zero-sequence voltage start-up threshold. When a single-phase ground fault is detected in the flexible interconnected distribution network, the control unit on that side immediately sends a fault start signal to control the activation of the fault feature enhancement module. Due to the zero-sequence path characteristics of the non-isolated flexible interconnection device 3, after the fault occurs, the zero-sequence voltage component will be transmitted through the flexible interconnection device 3, which usually causes the zero-sequence voltage of the busbars on both sides to exceed the zero-sequence voltage start threshold almost simultaneously. This causes the control units on both sides to activate the fault feature enhancement module almost simultaneously and continue the fault troubleshooting process in the following method embodiment.

[0077] What can be connected is the zero-sequence voltage start-up threshold. Used to assist in detecting whether a single-phase ground fault has occurred. Among them, the zero-sequence voltage initiation threshold... It needs to reliably avoid unbalanced voltages during normal system operation while ensuring sufficient sensitivity during faults. In one example, the zero-sequence voltage trigger threshold... The calculation formula is:

[0078] ;

[0079] in, The reliability factor is typically taken as 1.2 to 1.5. This is the system's rated phase voltage.

[0080] In one embodiment, the first grounding element and the second grounding element can be either a resistor or an inductor. In one example, the first grounding element is a resistor and the second grounding element is an inductor.

[0081] In one embodiment, the first fault feature enhancement module 11 and the second fault feature enhancement module 21 have the same structure, each including a resistor assembly and a control switch connected to the resistor assembly; the control switch is used to engage or disengage the resistor assembly.

[0082] It should be noted that the resistor assembly includes at least one resistor, and multiple resistors can be connected in series or parallel. The control switch can be connected in parallel or series with the resistor assembly. The resistance value of the resistor assembly can be adjusted according to system parameters. The control switch can be a fast switching device capable of withstanding system voltage and inrush current, and its specific configuration can be determined based on actual conditions. In one example, the control switch can use a power electronic switch such as a vacuum contactor or an insulated gate bipolar transistor (IGBT) to control the connection and disconnection of the resistor assembly. The first control unit 12 is connected to the control switch located on the first AC power distribution system 1 side, and outputs control commands to switch the on or off state of the control switch, thereby controlling the connection and disconnection of the resistor assembly. The second control unit 22 is connected to the control switch located on the second AC power distribution system 2 side, and outputs control commands to switch the on or off state of the control switch, thereby controlling the connection and disconnection of the resistor assembly. The on or off state of the control switch can be determined based on the connection relationship between the control switch and the resistor assembly, as well as the connection requirements of the resistor assembly.

[0083] This embodiment uses a resistor and a control switch connected in series as an example. Figure 1 As shown, Figure 1 Rinj represents a resistor assembly. At this time, there is only one resistor in the resistor assembly, and the resistor is connected in series with the control switch. When the resistor assembly needs to be activated, the first control unit 12 drives the control switch located on the first AC power distribution system 1 side to be turned on, and the second control unit 22 drives the control switch located on the second AC power distribution system 2 side to be turned on.

[0084] In one embodiment, the resistance value of the resistor component can be calculated based on the following formula.

[0085] ;

[0086] In the formula, The system's rated phase voltage, This represents the expected fault current.

[0087] In one example The current level is typically set between 50A and 100A. This range of current levels can significantly amplify fault characteristics while being limited to the thermal stability capacity of the grounding equipment. This allows the installed resistor components to significantly enhance fault characteristics while avoiding overheating.

[0088] In one embodiment, zero-sequence voltage transformers are installed on the busbars of the first AC power distribution system 1 and the second AC power distribution system 2, and zero-sequence current transformers are installed on each outgoing line of the first AC power distribution system 1 and the second AC power distribution system 2. The zero-sequence voltage transformers are used to collect the zero-sequence voltage of the busbars; the zero-sequence current transformers are used to collect the zero-sequence current of the outgoing lines.

[0089] Among them, the zero-sequence voltage transformer and the zero-sequence current transformer located in the first AC power distribution system 1 are respectively connected to the first control unit 12 and are used to transmit the zero-sequence voltage of the bus and the zero-sequence current of the outgoing line to the first control unit 12.

[0090] The zero-sequence voltage transformer and the zero-sequence current transformer located in the second AC power distribution system 2 are respectively connected to the second control unit 22 and are used to transmit the zero-sequence voltage of the bus and the zero-sequence current of the outgoing line to the second control unit 22.

[0091] It should be noted that a zero-sequence current transformer can record the amplitude and phase of the zero-sequence current in the outgoing line. A zero-sequence voltage transformer can record the waveform of the zero-sequence voltage in the bus.

[0092] In one embodiment, both the first control unit 12 and the second control unit 22 are equipped with a high-speed processor for performing fault judgment, logical operations and issuing control commands.

[0093] In one embodiment, the first control unit 12 can switch the first fault feature enhancement module 11 by setting a first control subunit. The second control unit 22 can switch the second fault feature enhancement module 21 by setting a second control subunit. The first and second control subunits have identical structures and can be implemented using logic gate circuits.

[0094] In one embodiment, such as Figure 2 As shown, the first control subunit and the second control subunit may include: a comparator, a D flip-flop, an NOT gate, and an AND gate;

[0095] The two inputs of the comparator are used to receive the zero-sequence voltage of the bus. and zero-sequence voltage start-up threshold ;

[0096] The comparator's output is connected to the C terminal of the D flip-flop;

[0097] The D terminal of the D flip-flop is used to receive a high-level signal;

[0098] The output of the D flip-flop is connected to the first input of the AND gate;

[0099] The input of the NOT gate is used to receive the control shutdown signal;

[0100] The output of the NOT gate is connected to the second input of the AND gate;

[0101] The output of the AND gate is connected to the control switch in the fault feature enhancement module.

[0102] It should be noted that, Figure 2 In this diagram, a "1" connected to the D terminal of the D flip-flop represents a high-level signal. T1 represents a control switch.

[0103] The above is a description of a flexible interconnected distribution network provided by an embodiment of the present invention. The following is a description of a ground fault protection method for a flexible interconnected distribution network provided by an embodiment of the present invention.

[0104] Please see Figure 3 , Figure 3 This is a flowchart illustrating a ground fault protection method for a flexible interconnected distribution network provided in an embodiment of the present invention.

[0105] This invention provides a ground fault protection method for a flexible interconnected distribution network, applicable to the AC distribution system on any side of the flexible interconnected distribution network. When a single-phase ground fault is detected, the method includes:

[0106] 101. Activate the fault characteristic enhancement module. The fault characteristic enhancement module is used to change the zero-sequence impedance characteristics.

[0107] It should be noted that when a single-phase ground fault is detected in either side of the AC power distribution system, it indicates that a single-phase ground fault will also be detected in the other side. At this time, the fault feature enhancement modules of both AC power distribution systems are activated almost simultaneously, thereby reducing the zero-sequence impedance of both systems. This changes the zero-sequence impedance characteristics of the system from predominantly capacitive to predominantly resistive, significantly increasing the current level at the grounding point and altering the current distribution of the zero-sequence network. This creates distinctive fault characteristics for subsequent zero-sequence current direction determination based on local quantities. Therefore, this step, by activating the fault feature enhancement module, strengthens the fault characteristics, thereby proactively intervening in single-phase ground faults and reducing the risk of protection maloperation.

[0108] In one embodiment, the fault characteristic enhancement module is connected in parallel across the two ends of the grounding element of the AC power distribution system, and the grounding element is connected between the neutral point of the AC power distribution system and the ground.

[0109] In one embodiment, the fault characteristic enhancement module includes a resistor assembly and a control switch connected to the resistor assembly;

[0110] A control switch is used to engage or disengage the resistor assembly.

[0111] It should be noted that the description of the fault feature enhancement module can be found in the foregoing embodiments, and will not be repeated here.

[0112] 102. Obtain and determine the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line; and take the outgoing line whose zero-sequence current direction is from the outgoing line to the bus as the target outgoing line.

[0113] It should be noted that, based on the power direction discrimination algorithm, the direction of the zero-sequence current of each outgoing line can be determined using the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line. The direction of the zero-sequence current of each outgoing line can be divided into two directions: one is from the outgoing line to the bus, and the other is from the bus to the outgoing line.

[0114] In this step, if it is determined that the direction of the zero-sequence current of the outgoing line is from the outgoing line to the busbar, then the outgoing line is the target outgoing line.

[0115] 103. When there is only one target outgoing line, and the amplitude of the zero-sequence current of the target outgoing line is greater than the preset current threshold, the target outgoing line is disconnected.

[0116] It should be noted that, as can be seen from the aforementioned steps, after determining the direction of the zero-sequence current in each outgoing line, the number of target outgoing lines in each outgoing line can be determined.

[0117] When there is only one target output line, and the magnitude I0 of the zero-sequence current of the target output line satisfies I0>I 0set This indicates that the fault belongs to the area of ​​the local AC power distribution system (i.e., within the zone), and it can be determined that the target outgoing line is the faulty line. Therefore, in this scenario where the fault is clearly identified within the zone, the faulty line can be directly disconnected to achieve fault isolation. Wherein, I 0set This is the current threshold. To improve the reliability of circuit breaker operation in low-resistance grounding systems, this current threshold must avoid the maximum unbalanced current and capacitive current during normal operation. It can generally be set to 10A to 30A, but the specific value needs to be adjusted based on actual on-site measurement data.

[0118] In one embodiment, cutting off the target exit line includes:

[0119] Output a trip command to the tripping mechanism of the target outgoing line, causing the tripping mechanism to perform a tripping operation.

[0120] It should be noted that each outgoing line is equipped with a corresponding tripping mechanism to perform tripping or closing operations. When the tripping mechanism performs a tripping operation, it indicates that the outgoing line has been disconnected; when the tripping mechanism performs a closing operation, it indicates that the outgoing line has resumed operation. In one example, the tripping mechanism can be a circuit breaker.

[0121] 104. When there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, a preset round-cutting strategy is adopted to sequentially cut all outgoing lines until the faulty object is identified.

[0122] It should be noted that when there is more than one target outgoing line, or even if there is only one target outgoing line, the amplitude of the zero-sequence current of that target outgoing line is not greater than the current threshold (i.e., I0 ≤ I). 0set This indicates that the fault is within the area, but the faulty line is unclear and cannot be directly and uniquely identified. Therefore, for scenarios where the fault within the area is unclear, this step uses a preset round-trip strategy to switch all outgoing lines in turn, thereby eliminating the possibility that each outgoing line is faulty, in order to identify the faulty object. The round-trip strategy includes the order of switching and the process of determining whether an outgoing line is a faulty line. Therefore, by using the round-trip strategy, each outgoing line can be checked one by one to see if it is a faulty line.

[0123] It is understandable that during the switching process in this step, there may be outgoing lines that are faulty, or there may be situations where none of the outgoing lines are faulty. Therefore, the faulty objects in this step can be divided into outgoing lines and non-outgoing lines, among which non-outgoing lines include the bus or the AC distribution system on the opposite side.

[0124] In this embodiment, when the faulty line cannot be uniquely identified, a round-cutting method is used to cut off the suspected lines one by one until the fault disappears, thereby reliably locating and isolating the fault, fundamentally solving the problem of protection maloperation caused by the transmission of zero-sequence components.

[0125] 105. When there is no target outgoing line, or when the faulty object is not an outgoing line object, lock out the tripping mechanism of all outgoing lines.

[0126] It should be noted that when there is no target outgoing line, it means that the zero-sequence current of all outgoing lines flows from the bus to the line. This indicates that the fault is not within the zone and may be in the AC distribution system on the other side or outside the grounding protection range of this side. In other words, the fault is an external fault. Therefore, in this scenario, only alarm information is recorded and the tripping command of all outgoing lines on this side is blocked to avoid the tripping mechanism of the outgoing lines from malfunctioning.

[0127] When the fault object is not an outgoing line object, it indicates that there may be a bus fault or a fault in the AC power distribution system on the other side. Therefore, only the alarm information is recorded, and the tripping command of all outgoing lines on this side is blocked to prevent the tripping mechanism of the outgoing line from malfunctioning.

[0128] Understandably, once the fault is isolated or all outgoing lines have been cleared, the fault feature enhancement module is deactivated to restore the system to its normal grounding mode, thus preventing the resistors in the fault feature enhancement module from overheating and being damaged due to prolonged current flow.

[0129] In this embodiment, when a single-phase ground fault occurs in the flexible interconnected distribution network, the zero-sequence component generated by the single-phase ground fault is conducted to the AC distribution systems on both sides based on the flexible interconnection equipment in the flexible interconnected distribution network, so that both AC distribution systems on both sides detect the single-phase ground fault. For any AC distribution system, when a single-phase ground fault is detected, the fault feature enhancement module is activated to change its own zero-sequence impedance characteristics and enhance the fault features, thereby providing basic support for the discrimination of the zero-sequence current direction of each outgoing line; then, by acquiring and based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line, the zero-sequence current direction of each outgoing line is determined, realizing the determination of the zero-sequence current direction of each outgoing line, and the outgoing line with the zero-sequence current direction flowing from the outgoing line to the bus is taken as the target outgoing line, providing technical support for the discrimination of the target outgoing line. Then, the present invention determines different protection strategies according to the number of target outgoing lines and the zero-sequence current amplitude. Specifically, when only one If there is a target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than the preset current threshold, the target outgoing line is determined to be a faulty line and the target outgoing line is disconnected. If there is more than one target outgoing line, or if there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, it indicates that the fault object is not clear. Therefore, a preset round-trip strategy is adopted to sequentially disconnect all outgoing lines until the fault object is determined, thereby reliably locating and isolating the fault. If there is no target outgoing line, or if the fault object is a non-outgoing line object, to avoid the fault not appearing on the outgoing line, the tripping mechanism of all outgoing lines is blocked to prevent false tripping caused by the fault of the AC distribution system on the other side.

[0130] Therefore, the ground fault protection method for flexible interconnected distribution networks provided in this embodiment solves the technical problem of poor reliability of existing ground fault protection methods for flexible interconnected distribution networks. Moreover, this invention does not require modification of the original control strategy of the flexible interconnected equipment, nor does it require the establishment of a high-speed communication channel between the protection devices on both sides of the flexible interconnected equipment, thus further improving reliability and economy.

[0131] Please see Figure 4 , Figure 4 This is a flowchart illustrating a ground fault protection method for a flexible interconnected distribution network provided in an embodiment of the present invention.

[0132] This invention provides a ground fault protection method for a flexible interconnected distribution network, applicable to the AC distribution system on any side of the flexible interconnected distribution network. When a single-phase ground fault is detected, the method includes:

[0133] 201. Activate the fault characteristic enhancement module. The fault characteristic enhancement module is used to change the zero-sequence impedance characteristics.

[0134] It should be noted that when a single-phase ground fault is detected in either side of the AC power distribution system, it indicates that a single-phase ground fault will also be detected in the other side. At this time, the fault feature enhancement modules of both AC power distribution systems are activated almost simultaneously, thereby reducing the zero-sequence impedance of both systems. This changes the zero-sequence impedance characteristics of the system from predominantly capacitive to predominantly resistive, significantly increasing the current level at the grounding point and altering the current distribution of the zero-sequence network. This creates distinctive fault characteristics for subsequent zero-sequence current direction determination based on local quantities. Therefore, this step, by activating the fault feature enhancement module, strengthens the fault characteristics, thereby proactively intervening in single-phase ground faults and reducing the risk of protection maloperation.

[0135] In one embodiment, the fault characteristic enhancement module is connected in parallel across the two ends of the grounding element of the AC power distribution system, and the grounding element is connected between the neutral point of the AC power distribution system and the ground.

[0136] In one embodiment, the fault characteristic enhancement module includes a resistor assembly and a control switch connected to the resistor assembly;

[0137] A control switch is used to engage or disengage the resistor assembly.

[0138] It should be noted that the description of the fault feature enhancement module can be found in the foregoing embodiments, and will not be repeated here.

[0139] 202. Obtain the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line.

[0140] It should be noted that the zero-sequence voltage of the bus can be collected using a zero-sequence voltage transformer, and the zero-sequence current of each outgoing line can be collected using a zero-sequence current transformer.

[0141] 203. Determine the instantaneous value of the zero-sequence current of each outgoing line based on the zero-sequence current of each outgoing line, and determine the instantaneous value of the zero-sequence voltage of the bus based on the zero-sequence voltage of the bus.

[0142] It should be noted that after obtaining the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line, analysis can be performed based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line to obtain the instantaneous values ​​of the corresponding zero-sequence voltage and zero-sequence current.

[0143] 204. The zero-sequence current direction coefficient is calculated based on the instantaneous values ​​of the zero-sequence current of each outgoing line and the instantaneous value of the zero-sequence voltage of the bus.

[0144] It should be noted that the zero-sequence current direction coefficient can be obtained by integrating the product of the instantaneous values ​​of the zero-sequence voltage and the zero-sequence current within one power frequency cycle, and then dividing the result by the power frequency cycle.

[0145] In one embodiment, the formula for calculating the zero-sequence current direction factor can be:

[0146] ;

[0147] In the formula, Let be the instantaneous value of the zero-sequence current of any outgoing line. denoted as , where is the instantaneous value of the zero-sequence voltage of the bus, T is the power frequency period, and D is the zero-sequence current direction coefficient.

[0148] Therefore, in this embodiment, by inputting the instantaneous value of the zero-sequence voltage of the bus into the above calculation formula, and inputting the instantaneous value of the zero-sequence current of each outgoing line into the above formula, the zero-sequence current direction coefficient of each outgoing line can be obtained. In one example, T can be 0.02.

[0149] 205. Based on the comparison results of the zero-sequence current direction coefficient and the preset threshold, determine the zero-sequence current direction of each outgoing line; and take the outgoing line with the zero-sequence current direction flowing from the outgoing line to the bus as the target outgoing line.

[0150] It should be noted that this step compares the zero-sequence current direction coefficient with a preset threshold. Based on the comparison result, it can be determined whether the zero-sequence current direction is from the outgoing line to the busbar or from the busbar to the outgoing line. The threshold is 0. In this step, if it is determined that the zero-sequence current direction of the outgoing line is from the outgoing line to the busbar, then that outgoing line is the target outgoing line.

[0151] In one embodiment, determining the zero-sequence current direction of each outgoing line in step 205 based on the comparison result of the zero-sequence current direction coefficient and a preset threshold specifically includes:

[0152] Determine whether the zero-sequence current direction coefficient is less than a preset threshold. If it is, determine that the direction of the zero-sequence current is from the outgoing line to the busbar; otherwise, determine that the direction of the zero-sequence current is from the busbar to the outgoing line.

[0153] It should be noted that after calculating the zero-sequence current direction coefficient D, the zero-sequence current direction coefficient D is compared with 0. If D < 0, the direction of the zero-sequence current of the outgoing line is determined to be from the outgoing line to the busbar. If D > 0, the direction of the zero-sequence current of the outgoing line is determined to be from the busbar to the outgoing line.

[0154] 206. When there is only one target outgoing line, and the amplitude of the zero-sequence current of the target outgoing line is greater than the preset current threshold, the target outgoing line is cut off.

[0155] It should be noted that, as can be seen from the aforementioned steps, after determining the direction of the zero-sequence current in each outgoing line, the number of target outgoing lines in each outgoing line can be determined.

[0156] When there is only one target output line, and the magnitude I0 of the zero-sequence current of the target output line satisfies I0>I0set This indicates that the fault belongs to the area of ​​the local AC power distribution system (i.e., within the zone), and it can be determined that the target outgoing line is the faulty line. Therefore, in this scenario where the fault is clearly identified within the zone, the faulty line can be directly disconnected to achieve fault isolation. Wherein, I 0set This is the current threshold. To improve the reliability of circuit breaker operation in low-resistance grounding systems, this current threshold must avoid the maximum unbalanced current and capacitive current during normal operation. It can generally be set to 10A to 30A, but the specific value needs to be adjusted based on actual on-site measurement data.

[0157] In one embodiment, cutting off the target exit line includes:

[0158] Output a trip command to the tripping mechanism of the target outgoing line, causing the tripping mechanism to perform a tripping operation.

[0159] It should be noted that each outgoing line is equipped with a corresponding tripping mechanism to perform tripping or closing operations. When the tripping mechanism performs a tripping operation, it indicates that the outgoing line has been disconnected; when the tripping mechanism performs a closing operation, it indicates that the outgoing line has resumed operation. In one example, the tripping mechanism can be a circuit breaker.

[0160] 207. When there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, a preset round-cutting strategy is adopted to sequentially cut all outgoing lines until the faulty object is identified.

[0161] It should be noted that when there is more than one target outgoing line, or even if there is only one target outgoing line, the amplitude of the zero-sequence current of that target outgoing line is not greater than the current threshold (i.e., I0 ≤ I). 0set This indicates that the fault is within the area, but the faulty line is unclear and cannot be directly and uniquely identified. Therefore, for scenarios where the fault within the area is unclear, this step uses a preset round-trip strategy to switch all outgoing lines in turn, thereby eliminating the possibility that each outgoing line is faulty, in order to identify the faulty object. The round-trip strategy includes the order of switching and the process of determining whether an outgoing line is a faulty line. Therefore, by using the round-trip strategy, each outgoing line can be checked one by one to see if it is a faulty line.

[0162] It is understandable that during the switching process in this step, there may be outgoing lines that are faulty, or there may be situations where none of the outgoing lines are faulty. Therefore, the faulty objects in this step can be divided into outgoing lines and non-outgoing lines, among which non-outgoing lines include the bus or the AC distribution system on the opposite side.

[0163] In this embodiment, when the faulty line cannot be uniquely identified, a round-cutting method is used to cut off the suspected lines one by one until the fault disappears, thereby reliably locating and isolating the fault, fundamentally solving the problem of protection maloperation caused by the transmission of zero-sequence components.

[0164] 208. When there is no target outgoing line, or when the faulty object is not an outgoing line object, lock out the tripping mechanism of all outgoing lines.

[0165] It should be noted that when there is no target outgoing line, it means that the zero-sequence current of all outgoing lines flows from the bus to the line. This indicates that the fault is not within the zone and may be in the AC distribution system on the other side or outside the grounding protection range of this side. In other words, the fault is an external fault. Therefore, in this scenario, only alarm information is recorded and the tripping command of all outgoing lines on this side is blocked to avoid the tripping mechanism of the outgoing lines from malfunctioning.

[0166] When the fault object is not an outgoing line object, it indicates that there may be a bus fault or a fault in the AC power distribution system on the other side. Therefore, only the alarm information is recorded, and the tripping command of all outgoing lines on this side is blocked to prevent the tripping mechanism of the outgoing line from malfunctioning.

[0167] Understandably, once the fault is isolated or all outgoing lines have been cleared, the fault feature enhancement module is deactivated to restore the system to its normal grounding mode, thus preventing the resistors in the fault feature enhancement module from overheating and being damaged due to prolonged current flow.

[0168] In this embodiment, when a single-phase ground fault occurs in the flexible interconnected distribution network, the zero-sequence component generated by the single-phase ground fault is conducted to the AC distribution systems on both sides based on the flexible interconnection equipment in the flexible interconnected distribution network, so that both AC distribution systems on both sides detect the single-phase ground fault. For any AC distribution system, when a single-phase ground fault is detected, the fault feature enhancement module is activated to change its own zero-sequence impedance characteristics and enhance the fault features, thereby providing basic support for the discrimination of the zero-sequence current direction of each outgoing line; then, by acquiring and based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line, the zero-sequence current direction of each outgoing line is determined, realizing the determination of the zero-sequence current direction of each outgoing line, and the outgoing line with the zero-sequence current direction flowing from the outgoing line to the bus is taken as the target outgoing line, providing technical support for the discrimination of the target outgoing line. Then, the present invention determines different protection strategies according to the number of target outgoing lines and the zero-sequence current amplitude. Specifically, when only one If there is a target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than the preset current threshold, the target outgoing line is determined to be a faulty line and the target outgoing line is disconnected. If there is more than one target outgoing line, or if there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, it indicates that the fault object is not clear. Therefore, a preset round-trip strategy is adopted to sequentially disconnect all outgoing lines until the fault object is determined, thereby reliably locating and isolating the fault. If there is no target outgoing line, or if the fault object is a non-outgoing line object, to avoid the fault not appearing on the outgoing line, the tripping mechanism of all outgoing lines is blocked to prevent false tripping caused by the fault of the AC distribution system on the other side.

[0169] Therefore, the ground fault protection method for flexible interconnected distribution networks provided in this embodiment solves the technical problem of poor reliability of existing ground fault protection methods for flexible interconnected distribution networks. Moreover, this invention does not require modification of the original control strategy of the flexible interconnected equipment, nor does it require the establishment of a high-speed communication channel between the protection devices on both sides of the flexible interconnected equipment, thus further improving reliability and economy.

[0170] It should be understood that, although Figures 3 to 4 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order in which these steps are executed; they can be performed in other orders. Figures 3 to 4 At least some of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0171] Please see Figure 5 Based on the ground fault protection method for a flexible interconnected distribution network provided in any of the above embodiments, the step of sequentially switching all outgoing lines using a preset switching strategy until the fault object is determined in this embodiment includes:

[0172] S1. Following the preset cutting sequence, cut one of the outgoing lines in sequence.

[0173] It should be noted that this step sorts the outgoing wires according to a preset cutting order, and then cuts them off sequentially. One outgoing wire is cut off at a time.

[0174] In one embodiment, the cutting order can be determined according to the outgoing line number, or by other sorting methods.

[0175] S2. Based on the time after the cut-off, after a preset time, obtain and determine whether the zero-sequence voltage of the bus is less than the preset voltage threshold. If yes, determine that the faulty object is an outgoing line and the rotational cutting ends; otherwise, jump to execute S3.

[0176] S3. Determine if the outgoing line is at the end of the sequence. If yes, determine that the faulty object is not an outgoing object. If not, jump to execute S1 to S2.

[0177] It should be noted that the voltage threshold in this step is the same as the zero-sequence voltage start-up threshold in the previous step.

[0178] After all outgoing lines are disconnected, a delay is made. During this time, the zero-sequence voltage of the bus is monitored to see if it drops below the zero-sequence voltage initiation threshold. If it does, it indicates that the disconnected outgoing line is a faulty line. Therefore, the switching process ends, and the faulty line remains in an off-state. If the zero-sequence voltage is still higher than the zero-sequence voltage initiation threshold, it indicates that the faulty line has not yet been eliminated. Therefore, the process continues to execute S1 to S2 until all outgoing lines have been eliminated. If the zero-sequence voltage is still higher than the zero-sequence voltage initiation threshold after all outgoing lines have been eliminated, it indicates that the fault may be on the bus or the AC distribution system on the opposite side (i.e., an external fault).

[0179] Understandably, in S3, if the outgoing line is not the last in the sequence, before jumping to execute S1-S2, the outgoing line can be closed first (if it is a permanent fault, it will not be closed again), or it can remain disconnected.

[0180] In one application example, such as Figure 6 As shown, Figure 6 In the diagram, Y represents yes and N represents no. The process of a ground fault protection method for a flexible interconnected distribution network provided in this application example may include:

[0181] Detecting zero-sequence voltage;

[0182] Determine if the zero-sequence voltage is greater than the start-up threshold. If not, proceed to the step of detecting the zero-sequence voltage. If yes, connect a parallel resistor. The resistor is connected in series with the IGBT device and then in parallel with the neutral point element. The neutral point element is connected in series between the neutral point and ground of the star connection of the transformer.

[0183] Detecting zero-sequence current;

[0184] Calculate the zero-sequence current direction factor D based on the zero-sequence current and zero-sequence voltage;

[0185] Determine whether the zero-sequence current direction coefficient D is less than 0;

[0186] If so, determine if a fault has occurred within the area. Then, determine if the fault within the area is clear. If so, determine the faulty line, trip the faulty line, disconnect the parallel resistor, and end. Otherwise, select the line to be switched in turn and perform the switching in turn. Determine if the zero-sequence voltage has returned to normal. If so, the switching in turn ends. Otherwise, select the next line to be switched in turn and jump to the switching in turn step.

[0187] If not, determine that a fault has occurred outside the zone, execute the lockout trip command, disconnect the parallel resistor, and end.

[0188] This invention does not require modification of the original control strategy of the flexible interconnection equipment, nor does it require the establishment of a high-speed communication channel between the protection devices on both sides of the flexible interconnection equipment. Instead, it configures independent active intervention devices (i.e., fault feature enhancement modules and control units) at the neutral point of the AC system on each side. Under fault conditions, parallel resistors are simultaneously applied to enhance fault features, and fault area identification is achieved by relying on the local quantity protection principle. When the faulty line cannot be uniquely determined, suspected lines are cut off one by one in a round-cutting manner until the fault disappears, thereby reliably locating and isolating the fault. Ultimately, it solves the problem of cross-side transmission of zero-sequence components caused by non-isolated flexible interconnection equipment, which leads to misjudgment and maloperation of the distribution network grounding protection, and improves the reliability of grounding fault protection in flexible interconnected distribution networks.

[0189] Please see Figure 7 , Figure 7 The diagram shows a structural block diagram of a ground fault protection device for a flexible interconnected distribution network provided by an embodiment of the present invention.

[0190] This invention provides a ground fault protection device for a flexible interconnected distribution network, applicable to the AC distribution system on any side of the flexible interconnected distribution network. The device includes:

[0191] The activation unit 301 is used to activate the fault feature enhancement module when a single-phase ground fault is detected. The fault feature enhancement module is used to change the zero-sequence impedance characteristics.

[0192] The determining unit 302 is used to acquire and determine the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line; and to designate the outgoing line whose zero-sequence current direction is from the outgoing line to the bus as the target outgoing line.

[0193] The first cut-off unit 303 is used to cut off the target outgoing line when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than a preset current threshold.

[0194] The second cut-off unit 304 is used to sequentially cut off all outgoing lines in turn using a preset round-cutting strategy when there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, until the fault object is determined.

[0195] The interlocking unit 305 is used to interlock the tripping mechanism of all outgoing lines when there is no target outgoing line, or when the faulty object is a non-outgoing line object.

[0196] In one embodiment, the second cutting unit 304 is used to perform the following steps:

[0197] S1. Following the preset cutting sequence, cut one of the outgoing lines in sequence;

[0198] S2. Based on the time after the disconnection, after a preset time, obtain and determine whether the zero-sequence voltage of the bus is less than the preset voltage threshold. If yes, determine that the faulty object is an outgoing line and the rotation disconnection ends; otherwise, jump to execute S3.

[0199] S3. Determine if the outgoing line is at the end of the sequence. If yes, determine that the faulty object is not an outgoing object. If not, jump to execute S1 to S2.

[0200] S1. Following the preset cutting sequence, cut one of the outgoing lines in sequence;

[0201] S2. Based on the time after the disconnection, after a preset time, obtain and determine whether the zero-sequence voltage of the bus is less than the preset voltage threshold. If yes, determine that the faulty object is an outgoing line and the rotation disconnection ends; otherwise, jump to execute S3.

[0202] S3. Determine if the outgoing line is at the end of the sequence. If yes, determine that the faulty object is not an outgoing object. If not, jump to execute S1 to S2.

[0203] In one embodiment, the determining unit 302 includes:

[0204] The first determining subunit is used to determine the instantaneous value of the zero-sequence current of each outgoing line based on the zero-sequence current of each outgoing line, and to determine the instantaneous value of the zero-sequence voltage of the bus based on the zero-sequence voltage of the bus.

[0205] The calculation sub-unit is used to calculate the zero-sequence current direction coefficient based on the instantaneous value of the zero-sequence current of each outgoing line and the instantaneous value of the zero-sequence voltage of the bus.

[0206] The second determining subunit is used to determine the direction of the zero-sequence current of each outgoing line based on the comparison result between the zero-sequence current direction coefficient and a preset threshold.

[0207] In one embodiment, the second determining subunit is used to determine whether the zero-sequence current direction coefficient is less than a preset threshold. If it is, the zero-sequence current direction is determined to be from the outgoing line to the busbar; otherwise, the zero-sequence current direction is determined to be from the busbar to the outgoing line.

[0208] Please see Figure 8 The present invention also provides an electronic device 40, including a processor 42 and a memory 44;

[0209] Memory 44 is used to store program code and transfer program code to processor 42;

[0210] The processor 42 is used to execute the methods provided in any of the above embodiments according to instructions in the program code.

[0211] It should be noted that the electronic device 40 may be a computer device. The electronic device 40 in this application may include one or more of the following components: a processor 42, a memory 44, and one or more application programs, wherein the one or more application programs may be stored in the memory 44 and configured to be executed by one or more processors 42, and the one or more application programs are configured to perform the method described in the above embodiment of a ground fault protection method for a flexible interconnected distribution network.

[0212] Processor 42 may include one or more processing cores. Processor 42 connects to various parts within the electronic device 40 using various interfaces and lines, and performs various functions and processes data of the electronic device 40 by running or executing instructions, programs, code sets, or instruction sets stored in memory 44, and by calling data stored in memory 44. Optionally, processor 42 may be implemented using at least one hardware form of Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), or Programmable Logic Array (PLA). Processor 42 may integrate one or a combination of several of the following: Central Processing Unit (CPU), Graphics Processing Unit (GPU), and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the displayed content; and the modem handles wireless communication. It is understood that the modem may also not be integrated into processor 42 and may be implemented separately using a communication chip.

[0213] The memory 44 may include random access memory (RAM) or read-only memory (ROM). The memory 44 can be used to store instructions, programs, code, code sets, or instruction sets. The memory 44 may include a program storage area and a data storage area. The program storage area may store instructions for implementing an operating system, instructions for implementing at least one function (such as touch functionality, sound playback functionality, image playback functionality, etc.), and instructions for implementing the various method embodiments described below. The data storage area may also store data created by the electronic device 40 during use.

[0214] Those skilled in the art will understand that Figure 8 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the electronic device to which the present application is applied. The specific electronic device may include more or fewer components than shown in the figure, or combine certain components, or have different component arrangements.

[0215] This invention also provides a computer-readable storage medium for storing program code for performing the methods provided in any of the above embodiments.

[0216] In summary, the present invention provides a ground fault protection method and related apparatus for flexible interconnected distribution networks, which has the following advantages:

[0217] 1) High reliability. When the direction judgment criteria are ambiguous or multiple lines show fault characteristics at the same time, the fault can be accurately located by the alternating switching method, avoiding false tripping or failure to operate.

[0218] 2) Good speed and efficiency. The switching process is fast and orderly, and fault location and isolation can be completed within seconds, meeting the power supply reliability requirements of the distribution network.

[0219] 3) Protect equipment safety. The parallel resistor assembly is only briefly engaged during a fault and is protected against overheating damage through a quick-release mechanism.

[0220] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0221] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0222] Furthermore, in the various embodiments of the present invention, the functional units can be integrated into one processing unit, or each functional unit can be a separate physical entity, or two or more functional units can be integrated into one processing unit. The integrated unit described above can be implemented in hardware or as a software functional unit.

[0223] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0224] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0225] It should also be noted that in the description of this invention, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0226] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ground fault protection method for a flexible interconnected distribution network, applied to the AC distribution system on any side of the flexible interconnected distribution network, characterized in that, When a single-phase ground fault is detected, the method includes: A fault feature enhancement module is deployed, which is used to change the zero-sequence impedance characteristics; The direction of the zero-sequence current of each outgoing line is determined based on the zero-sequence voltage of the busbar and the zero-sequence current of each outgoing line; and the outgoing line whose zero-sequence current direction is from the outgoing line to the busbar is taken as the target outgoing line. When there is only one target output line, and the amplitude of the zero-sequence current of the target output line is greater than a preset current threshold, the target output line is disconnected. When there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, a preset round-cutting strategy is adopted to sequentially cut all the outgoing lines until the faulty object is determined. When the target outgoing line does not exist, or when the faulty object is a non-outgoing line object, the tripping mechanism of all the outgoing lines is locked.

2. The method according to claim 1, characterized in that, The process of sequentially switching all outgoing lines using a preset switching strategy until a faulty object is identified includes: S1. Following the preset cutting sequence, cut one of the outgoing lines in sequence; S2. Based on the time after the cut-off, after a preset time, obtain and determine whether the zero-sequence voltage of the bus is less than the preset voltage threshold. If yes, determine that the faulty object is an outgoing line and the rotational cutting ends; otherwise, jump to execute S3. S3. Determine if the outgoing line is at the end of the sequence. If yes, determine if the faulty object is a non-outgoing object. If not, jump to execute S1 to S2.

3. The method according to claim 2, characterized in that, The step of determining the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the busbar and the zero-sequence current of each outgoing line includes: The instantaneous value of the zero-sequence current of each outgoing line is determined based on the zero-sequence current of each outgoing line, and the instantaneous value of the zero-sequence voltage of the bus is determined based on the zero-sequence voltage of the bus. The zero-sequence current direction coefficient is calculated based on the instantaneous value of the zero-sequence current of each outgoing line and the instantaneous value of the zero-sequence voltage of the bus. The direction of the zero-sequence current in each outgoing line is determined by comparing the zero-sequence current direction coefficient with a preset threshold.

4. The method according to claim 3, characterized in that, Determining the zero-sequence current direction of each outgoing line based on the comparison result of the zero-sequence current direction coefficient and a preset threshold includes: Determine whether the zero-sequence current direction coefficient is less than a preset threshold. If it is, determine that the direction of the zero-sequence current is from the outgoing line to the busbar; otherwise, determine that the direction of the zero-sequence current is from the busbar to the outgoing line.

5. The method according to claim 4, characterized in that, The fault feature enhancement module is connected in parallel to both ends of the grounding element of the AC power distribution system, and the grounding element is connected between the neutral point of the AC power distribution system and the ground.

6. The method according to claim 4, characterized in that, The fault feature enhancement module includes a resistor assembly and a control switch connected to the resistor assembly; The control switch is used to engage or disengage the resistor assembly.

7. A ground fault protection device for a flexible interconnected distribution network, applied to the AC distribution system on any side of the flexible interconnected distribution network, characterized in that, The device includes: The activation unit is used to activate the fault feature enhancement module when a single-phase ground fault is detected. The fault feature enhancement module is used to change the zero-sequence impedance characteristics. The determining unit is used to acquire and determine the direction of the zero-sequence current of each outgoing line based on the zero-sequence voltage of the bus and the zero-sequence current of each outgoing line; and to designate the outgoing line whose zero-sequence current direction is from the outgoing line to the bus as the target outgoing line. The first cut-off unit is used to cut off the target outgoing line when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is greater than a preset current threshold. The second cut-off unit is used to sequentially cut off all the outgoing lines in turn using a preset round-cutting strategy when there is more than one target outgoing line, or when there is only one target outgoing line and the amplitude of the zero-sequence current of the target outgoing line is not greater than the current threshold, until the fault object is determined. The interlocking unit is used to interlock the tripping mechanism of all outgoing lines when the target outgoing line does not exist, or when the faulty object is a non-outgoing line object.

8. A flexible interconnected distribution network, characterized in that, include: First AC power distribution system, second AC power distribution system, flexible interconnection equipment; The first AC power distribution system is connected to the flexible interconnection device, and is also connected to the second AC power distribution system through the flexible interconnection device; The neutral point of the first AC power distribution system is connected to one end of the first grounding element, and the other end of the first grounding element is grounded. The neutral point of the second AC power distribution system is connected to one end of the second grounding element, and the other end of the second grounding element is grounded. The first fault feature enhancement module is connected in parallel to both ends of the first grounding element; The second fault feature enhancement module is connected in parallel across the two ends of the second grounding element; The first fault feature enhancement module is connected to the first control unit; the second fault feature enhancement module is connected to the second control unit. The first control unit is configured to perform the method as described in any one of claims 1-6; The second control unit is used to perform the method as described in any one of claims 1-6.

9. An electronic device, characterized in that, Including the processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the method as described in any one of claims 1-6 according to instructions in the program code.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store program code for performing the method as described in any one of claims 1-6.

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