Protection method and device for active power distribution network

Abstract

The application provides a protection method and device of an active power distribution network. The method is applied to a protection device of a weak feed side, and comprises the following steps: collecting three-phase electric information in real time, and determining fault detection information according to the three-phase electric information; wherein the three-phase electric information represents an electrical quantity parameter at the installation position of the protection device, the fault detection information comprises a positive sequence current amplitude and a direction criterion, and the direction criterion represents the positional relationship of a fault point relative to the protection device; performing a protection operation according to the direction criterion, the positive sequence current amplitude, a preset current protection threshold value and the signal characteristics of a blocking signal from a system side; wherein the blocking signal is used to block the tripping circuit of the protection device, the preset current protection threshold value is greater than the maximum load current of the active power distribution network, and the protection operation is used to control the response behavior of the protection device of the weak feed side to the fault of the active power distribution network. The method is used to improve the reliability and stability of the fault protection of the active power distribution network.

Description

Technical Field

[0001] This application relates to the field of power system relay protection, and in particular to a protection method and device for an active distribution network. Background Technology

[0002] With the rapid development of new energy power generation technologies such as distributed photovoltaic and wind power, traditional distribution networks mainly powered by the main grid are gradually transforming into a structure of "weak main grid + multiple power sources". In this type of active distribution network, a large number of distributed power sources are connected, and the distribution network becomes an active network. The amplitude and direction of fault currents are uncertain, posing a challenge to traditional protection technologies.

[0003] In existing technologies, overcurrent protection or differential protection schemes are difficult to set due to the uncertainty of the amplitude and direction of the fault current, making them unsuitable for high-penetration distributed power supply access scenarios. Although directional longitudinal protection can determine the fault direction by relying on local electrical quantities and comprehensively determine the fault section by interacting with the other side, it also has the problem of refusing to operate the weak feeder protection when there is a high transition resistance fault and maloperation in non-fault sections, which may lead to failure of fault clearing or expansion of the power outage area.

[0004] Therefore, given the current problem of insufficient protection reliability in active distribution networks, there is an urgent need for a solution to improve the reliability of protection for active distribution networks in order to ensure the safe and stable operation of active distribution networks. Summary of the Invention

[0005] The active power distribution network protection method and apparatus provided in this application are used to improve the reliability and stability of fault protection for active power distribution networks.

[0006] In a first aspect, embodiments of this application provide a protection method for an active distribution network, the active distribution network including a weak feeder side and a system side, the method being applied to protection equipment on the weak feeder side, the method comprising:

[0007] The system collects three-phase electrical information in real time and determines fault detection information based on this information. The three-phase electrical information represents the electrical parameters at the installation location of the protection equipment, while the fault detection information includes the positive sequence current amplitude and direction criteria. The direction criteria represent the orientation of the fault point relative to the protection equipment.

[0008] Based on the direction criteria, positive sequence current amplitude, preset current protection threshold, and signal characteristics of the blocking signal from the system side, the protection operation is executed. The blocking signal is used to block the tripping circuit of the protection equipment. The preset current protection threshold is greater than the maximum load current of the active distribution network. The protection operation is used to control the response behavior of the protection equipment on the weak feeder side to faults in the active distribution network.

[0009] Optionally, as described above, the three-phase electrical information includes three-phase voltage information and three-phase current information; based on the three-phase electrical information, fault detection information is determined, including:

[0010] The three-phase voltage information and three-phase current information are filtered separately to determine the positive sequence voltage phasor corresponding to the three-phase voltage information and the positive sequence current phasor corresponding to the three-phase current information.

[0011] Determine the positive sequence current amplitude based on the positive sequence current phasor;

[0012] The direction criterion is determined based on the positive sequence voltage phasor and the positive sequence current phasor.

[0013] Determine the positive sequence current amplitude and direction criteria to provide fault detection information.

[0014] Optionally, as described above, the direction criterion is determined based on the positive-sequence voltage phasor and the positive-sequence current phasor, including:

[0015] Determine the positive-sequence phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor;

[0016] If the positive sequence phase difference is within the preset phase range, then the direction criterion characterizes the orientation relationship between the fault point and the protection device as the positive direction.

[0017] Optionally, as described above, the protection operation includes a stop-signal operation, which indicates that the blocking signal is stopped being sent to the system side; the protection operation is performed based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side, including:

[0018] Based on the positive sequence current amplitude and the preset current judgment threshold, the sending status of the blocking signal to the system side is determined; wherein, the preset current judgment threshold is less than the preset current protection threshold and greater than the maximum load current of the active distribution network.

[0019] Based on the transmission status, direction criteria, positive sequence current amplitude, preset current protection threshold, and signal characteristics, a signal stop operation is executed.

[0020] Optionally, as described above, the transmission status includes a transmission in progress status or a transmission stopped status; the transmission status for sending a blocking signal to the system side is determined based on the positive sequence current amplitude and a preset current judgment threshold, including:

[0021] If the positive sequence current amplitude is greater than the preset current judgment threshold, the transmission state is determined to be in progress.

[0022] If the positive sequence current amplitude is less than or equal to the current judgment threshold and a blocking signal is received from the system side within the preset communication time window, then the transmission state is determined to be the transmission in progress state.

[0023] If the positive sequence current amplitude is less than or equal to the current judgment threshold, and no blocking signal is received from the system side within the preset communication time window, then the transmission status is determined to be the transmission stop status.

[0024] Optionally, as described above, a signal termination operation is performed based on the transmission status, direction criterion, positive sequence current amplitude, preset current protection threshold, and signal characteristics, including:

[0025] If the transmission status is in progress, the direction criterion indicates that the orientation of the fault point relative to the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the first characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a signal stop operation is performed; wherein, the first characteristic condition indicates that the blocking signal received from the system side has reached the preset signal duration.

[0026] Optionally, the method described above further includes:

[0027] If the transmission status is in progress and the direction criterion indicates that the fault point is in a positive direction relative to the protection device, then a stop-transmission operation is performed.

[0028] Optionally, as described above, the protection operation includes a tripping operation, which indicates that a trip is performed to isolate the faulty section; the protection operation is performed based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side, including:

[0029] If the direction criterion indicates that the orientation relationship between the fault point and the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the second characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a trip operation is performed; wherein, the second characteristic condition indicates that a blocking signal is received in the first time period and no blocking signal is received in the second time period after the first time period.

[0030] Optionally, the method described above further includes:

[0031] If the direction criterion indicates that the fault point is in a positive direction relative to the protection device, and no blocking signal is received from the system side within the preset communication time window, then a tripping operation is performed.

[0032] Secondly, embodiments of this application provide a protection device for an active distribution network, the active distribution network including a weak feeder side and a system side, the device being applied to protection equipment on the weak feeder side, the device comprising:

[0033] The acquisition module is used to acquire three-phase power information in real time and determine fault detection information based on the three-phase power information. The three-phase power information represents the electrical quantity parameters at the installation location of the protection equipment, and the fault detection information includes the positive sequence current amplitude and direction criteria. The direction criteria represent the orientation relationship between the fault point and the protection equipment.

[0034] The execution module is used to perform protection operations based on the direction criteria, positive sequence current amplitude, preset current protection threshold, and signal characteristics of the blocking signal from the system side. The blocking signal is used to block the tripping circuit of the protection equipment, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation is used to control the response behavior of the protection equipment on the weak feeder side to faults in the active distribution network.

[0035] Thirdly, embodiments of this application provide an electronic device, including: a memory and a processor;

[0036] The memory stores the instructions that the computer executes;

[0037] The processor executes computer execution instructions stored in memory, causing the processor to perform the first aspect and / or various possible implementations of the first aspect as described above.

[0038] Fourthly, embodiments of this application provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the first aspect and / or various possible implementations of the first aspect.

[0039] Fifthly, embodiments of this application provide a computer program product, including a computer program that, when executed by a processor, implements the first aspect and / or various possible implementations of the first aspect.

[0040] This application provides a protection method and apparatus for an active distribution network, which includes a weak feeder side and a system side. The method is applied to the protection equipment on the weak feeder side. The method involves real-time acquisition of three-phase electrical information and determination of fault detection information based on this information. The three-phase electrical information represents the electrical parameters at the installation location of the protection equipment. The fault detection information includes the positive sequence current amplitude and direction criterion, with the direction criterion representing the orientation of the fault point relative to the protection equipment. Further, protection operations are executed based on the direction criterion, the positive sequence current amplitude, a preset current protection threshold, and the signal characteristics of a blocking signal from the system side. The blocking signal is used to block the tripping circuit of the protection equipment, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation controls the response behavior of the protection equipment on the weak feeder side to faults in the active distribution network. The active distribution network protection method provided in this application introduces positive-sequence current amplitude as the core criterion for weak-feed side protection, replacing the traditional criterion method that relies on voltage thresholds. This avoids the risk of weak-feed side failure to operate due to unclear voltage characteristics under high transition resistance faults. By combining the dual constraints of direction criterion and positive-sequence current amplitude, and introducing the signal characteristics of blocking signals from the system side as auxiliary discrimination criteria, the method distinguishes the differences between the faulty section and the downstream non-faulty section during signal interaction, reducing the risk of maloperation in non-faulty sections due to misjudgment of direction. By fusing the positive-sequence current amplitude, direction criterion, and signal characteristics of blocking signals into a fusion decision, the weak-feed side protection equipment can still accurately perform protection operations under complex operating conditions of active distribution networks with weak fault current amplitude and uncertain direction. The method in this application improves the reliability and stability of fault protection in active distribution networks. Attached Figure Description

[0041] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0042] Figure 1 Scenario illustration provided for this application Figure 1 ;

[0043] Figure 2 Scenario illustration provided for this application Figure 2 ;

[0044] Figure 3 Scenario illustration provided for this application Figure 3 ;

[0045] Figure 4 Scenario illustration provided for this application Figure 4 ;

[0046] Figure 5 Flowchart of the protection method for active power distribution networks provided in this application Figure 1 ;

[0047] Figure 6 Flowchart of the protection method for active power distribution networks provided in this application Figure 2 ;

[0048] Figure 7 A schematic diagram of the protection operation provided for this application Figure 1 ;

[0049] Figure 8 A schematic diagram of the protection operation provided for this application Figure 2 ;

[0050] Figure 9 A schematic diagram of the protection operation provided for this application Figure 3 ;

[0051] Figure 10 A schematic diagram of the protection operation provided for this application Figure 4 ;

[0052] Figure 11 A schematic diagram of the protection operation provided for this application Figure 5 ;

[0053] Figure 12 A schematic diagram of the protection operation provided for this application Figure 6 ;

[0054] Figure 13 A schematic diagram of the structure of the protection device for the active power distribution network provided in this application;

[0055] Figure 14 A schematic diagram of the structure of the electronic device provided in this application.

[0056] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0057] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0058] It should be noted that the data involved in this application (including but not limited to data used for analysis, data stored, data displayed, etc.) are all information and data that have been fully authorized by all parties, and the collection, use, processing, transmission, provision, disclosure and application of the relevant data shall comply with relevant laws, regulations and standards.

[0059] It should be noted that the active distribution network protection method and device of this application can be used in the field of power system relay protection, or in any field other than power system relay protection. The application field of the active distribution network protection method and device of this application is not limited.

[0060] First, let me explain the terms used in this application:

[0061] Distributed generation (DG) refers to small-capacity, dispersed power generation units connected to the distribution network. These typically include photovoltaic power generation, wind power generation, small gas turbines, fuel cells, and energy storage devices. Their installed capacity is generally between several kilowatts and tens of megawatts. They can directly supply power to the distribution network or loads, changing the traditional one-way power receiving operation mode of the distribution network.

[0062] Inverter Interfaced Distributed Generator (IIDG) refers to a type of distributed power source that uses a power electronic inverter to achieve an electrical interface with the distribution network.

[0063] With the widespread integration of photovoltaic, wind power, energy storage power sources, and various inverter power sources into 10 kV and below distribution networks, the traditional network structure of unidirectional power transmission from substation busbars to downstream feeders has gradually evolved into a network configuration where the system side and weak feeder side coexist, multiple power sources are distributed, and local power flow changes bidirectionally. In this type of application environment, protection devices are typically distributed and installed at both ends of the line, branch nodes, or sectionalizing switches. By collecting electrical information such as three-phase voltage and three-phase current at the installation points, they determine the direction of the fault, the fault section, and whether tripping should be performed. They also exchange blocking signals with relevant devices on the system side to ensure that the fault section can be quickly isolated after a fault occurs and that continuous power supply to the non-faulty sections can be maintained.

[0064] In existing active distribution network protection, common solutions include overcurrent protection, differential protection, and directional longitudinal protection.

[0065] Overcurrent protection mainly relies on the local current amplitude exceeding the set value to determine the fault. However, after the distributed power source is connected, the fault current may be provided by both the system side and the distributed power source side. The current direction and amplitude change with the operating mode, output level and fault location. The original fixed setting value is difficult to maintain stable application and is prone to false tripping or failure to trip in reverse feed or short circuit current limited scenarios.

[0066] Differential protection identifies faults within a region by comparing the current difference on both sides of a line. In principle, it has high selectivity, but it has high requirements for communication links, data synchronization, and measurement integrity. In the distribution network, when encountering T-connected branches, unmeasurable load branches, communication delay fluctuations, etc., the differential current balance is easily disrupted, and the engineering deployment cost and operation and maintenance difficulty are also relatively large.

[0067] Directional longitudinal protection achieves fault isolation by coordinating local direction discrimination with blocking signals from the opposite side, and has a certain application basis in engineering. However, it also faces obvious defects in active distribution networks: On the one hand, the local voltage characteristics of the weak feeder side are often not obvious under high transition resistance faults, and the sensitivity of traditional direction and stop signal criteria that rely on voltage changes or single electrical quantities decreases, causing the protection devices that should assist in clearing the fault to remain in a blocked state. On the other hand, non-faulty sections may experience directional misjudgment due to load current crossing, reverse transmission of short-circuit current from downstream distributed power sources, and changes in fault current distribution, which may lead to maloperation during changes in the blocking signal.

[0068] In addition, some solutions rely on strong communication synchronization conditions. When the transmission of blocking information is interfered with, the reliability and selectivity of the protection action will further decrease.

[0069] In view of this, how to improve the fault identification accuracy of weak feeder protection equipment under the condition of distributed power supply access, and take into account the reliability of fault section isolation and the selectivity of non-fault sections, has become an urgent technical problem to be solved.

[0070] Based on the foregoing, the following is a quantitative analysis of the steady-state characteristics of active distribution network faults under weak feeder conditions, provided by the inventors:

[0071] Figure 1 Scenario illustration provided for this application Figure 1 ,like Figure 1As shown, this scenario presents a schematic diagram of a distribution network structure with multiple IIDGs connected. Taking a 10kV distribution network as an example, bus A is close to the system power source and is the connection point of the 10kV bus of the substation or the feeder of the main grid. Bus D is close to the load and is the end of the line or a concentrated load area. Each of the buses B, C, and D of this distribution network is connected to an IIDG, namely IIDG1, IIDG2, and IIDG3, respectively. Protection devices 1, 3, and 5 are defined as protection devices on the system side, and protection devices 2, 4, and 6 are defined as protection devices on the weak feeder side. It is assumed that the fault occurs between the BC lines, and the fault point is f.

[0072] Based on the above distribution network structure, the establishment of a fault equivalent model can include the following steps:

[0073] The system power supply is equivalent to a voltage source. With impedance In the series connection, since the positive-sequence impedance and negative-sequence impedance on the system side are not significantly different, for the sake of simplifying the analysis, we assume they are equal; the positive-sequence impedance and negative-sequence impedance of lines AB and CD are both equal, and are expressed as follows: and The line impedances from bus B and bus C to the fault point f are expressed as follows: and The load impedance is IIDG1 to IIDG3 employ active and reactive power decoupling control, suppressing negative sequence components and possessing low voltage ride-through capability. They are equivalent to voltage-controlled current sources controlled by the positive sequence voltage at the grid connection point, with no negative sequence output. The positive and negative sequence voltages at the fault point are respectively expressed as... and .

[0074] exist Figure 1 On this basis, Figure 2 Scenario illustration provided for this application Figure 2 , Figure 3 Scenario illustration provided for this application Figure 3 When a two-phase short circuit occurs in the system, its positive-sequence and negative-sequence equivalent networks are as follows: Figure 2 and Figure 3 As shown.

[0075] exist Figure 2 In the diagram, the current and voltage corresponding to IIDG1 can be expressed as follows: and The current and voltage corresponding to IIDG2 can be expressed as follows: and The current and voltage corresponding to IIDG3 can be expressed as follows: and .

[0076] In a positive sequence network, the system power supply is equivalent to a voltage source. With impedance Series connection, system voltage source The positive sequence current is provided to the fault point through the line impedance. Each IIDG acts as a voltage-controlled current source and outputs a controlled current according to the positive sequence voltage at its grid connection point. Load impedance As a positive-sequence equivalent impedance connected to the network, the positive-sequence voltage at the fault point is expressed as: .

[0077] exist Figure 3 In the negative-sequence network, since IIDG1 to IIDG3 employ a negative-sequence suppression control strategy, there is no negative-sequence current output. Therefore, the negative-sequence network does not contain the equivalent current source of IIDG. The negative-sequence voltage source only exists at the fault point, and the system-side and load-side impedances form a path for the negative-sequence current. Load impedance As a negative-sequence equivalent impedance connected to the network, the negative-sequence voltage at the fault point is expressed as: .

[0078] Based on the foregoing embodiments, Figure 4 Scenario illustration provided for this application Figure 4 From the boundary conditions of a two-phase short-circuit fault, it can be seen that the positive sequence voltage at the fault point is equal to the negative sequence voltage, and the composite sequence network is as follows: Figure 4 As shown.

[0079] exist Figure 4 In the network, the positive-sequence network and the negative-sequence network are connected in parallel at the fault point to form a composite-sequence network. The positive-sequence voltage at the fault point... With negative sequence voltage The positive-sequence current and the negative-sequence current are equal, and the sum of them satisfies the fault boundary conditions. Looking from the fault point to both sides, the system-side branch impedance is the sum of the impedance of the system power supply, the impedance of line AB, and the impedance from bus B to the fault point f. The load-side branch impedance is the sum of the impedance from bus C to the fault point f, the impedance of line CD, and the load impedance.

[0080] Negative sequence equivalent impedance can be expressed as Its value can satisfy:

[0081] ;

[0082] in, Indicates the impedance of the system power supply. This represents the impedance of line AB. This represents the impedance from bus B to the fault point f. This represents the impedance from bus C to the fault point f. This indicates the impedance of line CD. Indicates load impedance. This represents the parallel operation of impedances.

[0083] It is understandable that during a three-phase short circuit, only the positive-sequence component exists, while the negative-sequence equivalent impedance remains. It is 0.

[0084] Furthermore, a quantitative analysis of the fault steady-state characteristics can be performed, which can be:

[0085] Upstream of the fault point, the short-circuit current supplied by the system power supply is typically no less than three times the rated current, while the maximum output current of the IIDG is 1.2 to 1.5 times the rated current. Even in extreme scenarios with 100% penetration, the connection of the IIDG has minimal impact on the phase difference between the voltage and current measured by the protection system. Its power direction is entirely towards the fault point, and the minimum current amplitude is the difference between the minimum short-circuit current supplied by the system power supply and the maximum output current of the IIDG, which is 1.5 times the rated current, far exceeding the maximum load current. .

[0086] Downstream of the fault point, when the fault is a two-phase short circuit, due to the load impedance... Typically much larger than the line impedance, the downstream line impedance can be... , , The sum of these values ​​is ignored, meaning the impedance from bus C to fault point f, the impedance of line CD, and the load impedance are all ignored. If the transition resistance is not considered, then... Figure 4 In the middle, it can satisfy:

[0087] ;

[0088] in, Indicates the negative sequence equivalent impedance. Indicates the impedance of the system power supply. This represents the impedance of line AB. This represents the impedance from bus B to the fault point f.

[0089] At this time, the positive sequence voltage at the fault point It can satisfy:

[0090] ;

[0091] in, This represents the positive sequence voltage at the fault location. Indicates the negative sequence equivalent impedance. Indicates the voltage source of the system power supply. Indicates the impedance of the system power supply. This represents the impedance of line AB. This represents the impedance from bus B to the fault point f.

[0092] When the output of the distributed power source downstream of the fault point is 0, the positive sequence current passing through bus C at the fault point... The maximum value is reached at this point. It can be represented as:

[0093] ;

[0094] in, This represents the positive sequence current passing through bus C at the fault point. This represents the positive sequence voltage at the fault location. Indicates the voltage source of the system power supply. This represents the load impedance.

[0095] Positive sequence voltage at protection device 4 It can satisfy:

[0096] ;

[0097] in, This indicates the positive sequence voltage at point 4 of the protection device. This represents the positive sequence voltage at the fault location. This represents the positive sequence current passing through bus C at the fault point. This represents the impedance from bus C to the fault point f.

[0098] Maximum load current of the line Approximately This refers to the current value under rated load operation. Therefore, it can be seen that when a two-phase short circuit occurs, the maximum positive sequence current flowing downstream of the fault point is much smaller than the maximum load current, and the positive sequence voltage at protection device 4 is less than 0.5 times the rated voltage. As the capacity of IIDG2 and IIDG3 downstream of the fault point increases, the grid connection voltage will rise. According to the low voltage ride-through requirement, the distributed power source output current is approximately 0.8 times the rated current. When the distributed power source penetration rate is 100%, the maximum current it provides to the fault point is 0.8 times the maximum line load current. At this time, the amplitude of the positive sequence current flowing through protection devices 4, 5, and 6 is the current provided by the distributed power source minus the fault point ride-through current, which is much smaller than the maximum line load current, and the positive sequence power direction is towards the fault point. When the distributed power source penetration rate continues to increase, the direction of the positive sequence current flowing through protection devices 4, 5, and 6 is still towards the fault point, and the amplitude may be greater than the maximum line load current.

[0099] If transition resistance is considered, the transition resistance of a phase-to-phase short circuit is generally no more than 30 ohms (Ω), which will increase the fault equivalent impedance. Increase to At this time, the positive sequence voltage at the fault point is:

[0100] ;

[0101] in, This represents the positive sequence voltage at the fault location. Indicates the voltage source of the system power supply. Indicates the impedance of the system power supply. This represents the impedance of line AB. This represents the impedance from bus B to the fault point f. Indicates the transition resistance. This represents the negative sequence equivalent impedance.

[0102] The fault current is:

[0103] ;

[0104] in, This represents the through current at the fault point. Indicates the voltage source of the system power supply. Indicates the impedance of the system power supply. This represents the impedance of line AB. This represents the impedance from bus B to the fault point f. Indicates the transition resistance. This represents the negative sequence equivalent impedance.

[0105] Compared to metallic short circuits, the fault-point through-current is significantly increased. Therefore, when IIDG penetration is low, the positive-sequence power flows towards the load side, and the positive-sequence current amplitude is the through-current minus the current provided by the distributed generation, which will still be less than the maximum load current. As IIDG penetration increases, the positive-sequence power flows towards the fault point, and the positive-sequence current amplitude may be greater than or less than the maximum load current.

[0106] Downstream of the fault point, when the fault is a three-phase short circuit, if the transition resistance is not considered, the positive sequence power flows towards the fault point, and the positive sequence current amplitude is the maximum current output by the IIDG, which depends on the IIDG penetration rate and may be greater than or less than the maximum load current. If the transition resistance is considered... The short-circuit current supplied by the power source is shunt between the transition resistance and the load impedance. The larger the transition resistance, the larger the current flowing to the load side. When the transition resistance is 30Ω, and the minimum load impedance is calculated to be approximately 12Ω based on the maximum line load current of 500A, the current flowing to the load side is 0.7 times the short-circuit current on the power source side. Since the short-circuit current on the power source side is also relatively small, at 1.4 times the maximum load current, the current flowing to the load side is 0.98 times the maximum load current. The output currents of IIDG2 and IIDG3 are shunt between the equivalent impedance upstream of the fault point, the transition resistance, and the load impedance. Because the total parallel impedance of the equivalent impedance upstream of the fault point and the transition resistance is much smaller than the load impedance, almost all of the output currents of IIDG2 and IIDG3 flow to the fault point. Therefore, depending on the penetration rate of distributed power sources, the positive-sequence power downstream of the fault point may flow towards the load side or the fault point, but the magnitude of the positive-sequence current is always less than the maximum load current.

[0107] After different types of faults occur in the distribution network, they are all accompanied by a sudden drop in voltage. After a rapid change of about 40 milliseconds (ms), the transient process basically disappears, and the positive sequence voltage drops to the steady-state value. Its amplitude is proportional to the fault distance, but is usually less than 0.7 times the rated voltage. After system disturbances such as load surges and recovery from faults at remote ends of the main grid, as the penetration rate of distributed power sources increases, the system inertia decreases, and the system recovery time becomes longer, possibly even reaching minutes. However, the overall change is slow, and the voltage on the distribution network side (i.e., the weak feeder side) usually changes to 90% of the rated voltage 100 milliseconds after the disturbance occurs.

[0108] Furthermore, the description of the steady-state positive-sequence component characteristics of the fault can include:

[0109] Feature Description 1: The positive sequence power upstream of the fault point flows towards the fault point, and the current amplitude is much greater than the maximum load current. The positive sequence voltage drops to varying degrees due to the strong power supply of the system, and the transition resistance has a limited impact on it.

[0110] Feature Description 2: The direction and magnitude of positive-sequence power downstream of the fault point are strongly correlated with the magnitude of the transition resistance and the penetration rate of distributed power sources. When the positive-sequence power flows towards the fault point, the positive-sequence current magnitude may be greater than or less than the maximum load current; when the positive-sequence power flows towards the load side, the positive-sequence current magnitude is less than the maximum load current. The positive-sequence voltage exhibits significant uncertainty; it is generally lower than 0.5 times the rated voltage in metallic faults, but will be significantly increased when there is a transition resistance or extremely high distributed power source penetration.

[0111] Feature Description 3: If the voltage measurement time window is set to 100 milliseconds, when the system is disturbed, the voltage change within 100 milliseconds will be less than 10% of the rated voltage, while when the system is faulty, the voltage change within 100 milliseconds will be 30% of the rated voltage.

[0112] Based on this, the preliminary protection logic for an active power distribution network may include:

[0113] Weak feed side signaling logic: Signaling is initiated when the current exceeds 1.2 times the rated current or when signaling is initiated remotely;

[0114] Weak feeder side stop signal logic: Logic element Y1 has an output (indicating that the protection starting element on this side has been activated and the directional element determines that the fault is in the positive direction) or simultaneously meets the following conditions: logic element Y1 does not activate (indicating that the protection starting element on this side has not been activated or the directional element determines that the fault is not in the positive direction), continuously receives a blocking signal for 5 to 7 milliseconds, and at least one phase or phase-to-phase voltage is lower than 0.5 times the rated voltage.

[0115] Weak feeder side operation logic: No blocking signal is received and logic element Y1 has an output, or at least one phase or phase-to-phase voltage is lower than 0.5 times the rated voltage, no blocking signal is received and logic element Y1 does not operate.

[0116] Based on this, when a phase-to-phase short-circuit fault occurs in the fault section CD, the problems with the above preliminary protection logic may include:

[0117] Question 1: If there is a transition resistance at the fault point, according to feature description 1, the power supply side protection of the faulty line will stop issuing blocking signals; according to feature description 2, the weak feeder side signal interruption logic may meet the requirements, thus stopping the issuance of blocking signals, and the weak feeder side action logic may fail to operate because the voltage condition is not met (i.e., the positive sequence voltage is higher than 0.5 times the rated voltage, and the voltage criterion fails).

[0118] Question 2: According to feature description 2, if the positive sequence power flows towards the fault point in the downstream non-fault section CD, and the positive sequence current flowing through it is between 1.2 and 2 times the maximum load current, the transmitting element will operate but the protection starting element will not operate. The weak feeder side's stop signal logic may meet the requirement to stop transmitting the blocking signal, and its weak feeder side protection may meet the operating logic, leading to maloperation of the downstream non-fault section.

[0119] Therefore, addressing the current issue of insufficient protection reliability in active distribution networks, this application provides a protection method for active distribution networks. By introducing the positive-sequence current amplitude as the core criterion for weak-feed side protection, it replaces the traditional voltage threshold-based criterion, thus mitigating the risk of weak-feed side failure to operate due to indistinct voltage characteristics under high transition resistance faults. By combining the dual constraints of direction criterion and positive-sequence current amplitude, and introducing the signal characteristics of the blocking signal from the system side as an auxiliary discrimination criterion, it distinguishes the differences between the faulty section and the downstream non-faulty section during signal interaction, reducing the risk of maloperation in non-faulty sections due to misjudgment of direction. By fusing the positive-sequence current amplitude, direction criterion, and the signal characteristics of the blocking signal for decision-making, the weak-feed side protection equipment can still accurately perform protection operations under complex operating conditions of active distribution networks with weak fault current amplitude and uncertain direction. This method improves the reliability and stability of fault protection in active distribution networks.

[0120] The technical solution of this application and how it solves the above-mentioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0121] Figure 5 Flowchart of the protection method for active power distribution networks provided in this application Figure 1 The active power distribution network includes a weak feeder side and a system side. This method is applied to the protection equipment on the weak feeder side. The execution entity of this method can be the processor, controller, or embedded computing unit of the protection equipment, such as... Figure 5 As shown, the method includes:

[0122] S501. Real-time acquisition of three-phase power information, and determination of fault detection information based on the three-phase power information; wherein, the three-phase power information represents the electrical quantity parameters at the installation location of the protection equipment, and the fault detection information includes the positive sequence current amplitude and direction criterion, and the direction criterion represents the orientation relationship between the fault point and the protection equipment.

[0123] S502. Based on the direction criterion, positive sequence current amplitude, preset current protection threshold, and signal characteristics of the blocking signal from the system side, perform protection operation; wherein, the blocking signal is used to block the tripping circuit of the protection device, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation is used to control the response behavior of the protection device on the weak feeder side to the fault of the active distribution network.

[0124] In this context, an active distribution network refers to a distribution network that includes distributed generation access. This network includes both traditional power supply modes where the system side supplies power downstream, and scenarios where downstream distributed generation supplies power upstream. The system side is the power supply side corresponding to the weak feeder side. Its protection equipment (also called protection devices) can send blocking signals to the weak feeder side during faults to participate in vertical coordination.

[0125] The weak feeder side can refer to the side of an active distribution network that is far from the main grid and has relatively weak power supply capacity. At lines, branch nodes, or sectionalizing switches with distributed generation access, the weak feeder side is more susceptible to the effects of short-circuit current limitation, insignificant fault characteristics, and bidirectional power flow changes.

[0126] The system side can refer to the side of an active distribution network that connects to the substation bus or the main grid and has strong short-circuit capacity and stable voltage support capability. It can provide relatively clear fault current and voltage characteristics during a fault, and its protection equipment is usually the dominant side or the strong power supply side in a locked longitudinal protection system.

[0127] Protection equipment can refer to equipment installed on the weak feed side or system side for implementing protection judgment and action. It typically includes voltage transformers or voltage tapping units, current transformers or current tapping units, analog-to-digital conversion units, digital signal processing units, logic judgment units, communication interfaces, and trip execution circuits.

[0128] In the architecture of a blocking-type directional longitudinal protection system, the weak-feed side protection device and the system-side protection device exchange blocking signals via a communication link. When the system-side protection device detects a fault, it sends a blocking signal to the weak-feed side. The weak-feed side protection device receives this signal and accordingly blocks or opens its own tripping circuit. When the fault is located on the line between the two protection devices, the system-side protection device determines it to be a forward fault and stops sending blocking signals. The weak-feed side protection device, after confirming there is no blocking signal and that the tripping conditions are met, performs a trip, thus isolating the faulty section. This application mainly optimizes the protection logic of the weak-feed side protection device to solve the technical problems of the weak-feed side easily failing to operate during high transition resistance faults and easily maloperating in non-faulty sections.

[0129] In step S501, the three-phase electrical information can refer to the three-phase voltage and three-phase current related information collected at the installation location of the protection equipment. This information can be either instantaneous sampled values ​​or discrete phasor data calculated using one or more power frequency cycles. For example, the three-phase electrical information can be collected using sensors such as electromagnetic or electronic voltage transformers and current transformers.

[0130] Fault detection information can refer to a set of electrical quantity parameters and logical judgment results used to determine whether a fault has occurred at the installation location of the protection equipment and the location of the fault. It can include at least the positive sequence current amplitude and direction criteria, and optionally also auxiliary information such as negative sequence current amplitude, negative sequence direction criteria, voltage change, and power direction.

[0131] The positive sequence current amplitude can refer to the magnitude of the positive sequence current phasor. The positive sequence current amplitude is used to reflect the strength of the fault current. It can still provide a stable quantitative basis in the scenario where the fault current is limited on the weak feeder side. Therefore, it serves as the core constraint condition for the protection shutdown and tripping logic on the weak feeder side, replacing the reliance on voltage thresholds in the traditional scheme.

[0132] In practice, the protection device can continuously and synchronously sample the three-phase voltage and three-phase current at the installation point. The sampling frequency can be set to several tens to several hundred points per cycle according to the hardware capability of the protection device, so as to ensure that sufficient electrical characteristics can be extracted during both the transient and steady-state processes of the fault.

[0133] In one possible implementation, the acquired raw data can first be filtered to remove interference from DC offset, high-frequency noise, and harmonic components. The filtering method can be a Fourier algorithm, a cosine filtering algorithm, a low-pass filtering algorithm, or a phasor extraction algorithm based on a sliding data window. Further, the three-phase current can be decomposed using the symmetrical component method to obtain the positive-sequence current phasor; the three-phase voltage can also be decomposed using the symmetrical component method to obtain the positive-sequence voltage phasor. The magnitude of the positive-sequence current can be determined by the magnitude of the positive-sequence current phasor, i.e., by taking the square root of the sum of the squares of the real and imaginary parts of the positive-sequence current, or directly output by the phasor algorithm.

[0134] Direction criteria refer to the logical result of determining the relative location of a fault point based on the phase relationship between voltage and current at the installation location of the protection equipment. For example, pointing from one end of a line to the other is defined as the positive direction, and vice versa. Direction criteria are used to reflect whether the fault point is located on the positive or negative side of the protection equipment, thus providing a basis for subsequent protection actions.

[0135] In one possible implementation, the direction criterion can be generated based on the phase relationship between the positive-sequence voltage phasor and the positive-sequence current phasor. Specifically, the phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor is calculated, and then compared with a pre-set direction interval. When the phase difference falls into the positive direction determination interval, it indicates that the fault point is located in the positive direction of the protection device, and the direction criterion output is positive. When the phase difference falls into the negative direction determination interval, it indicates that the fault point is located on the back side of the protection device or in a fault section outside this side, and the direction criterion output is negative. For situations where the fault is in a boundary region or where the voltage is extremely low, leading to phase instability, the protection device can also combine the judgment results of multiple consecutive sampling windows to form a stable direction criterion, in order to avoid misjudgment caused by fluctuations in a single sampling window.

[0136] It is understandable that, since IIDGs typically employ active and reactive power decoupling control and negative sequence suppression strategies, their fault current output characteristics differ significantly from those of synchronous generators. Traditional directional elements designed based on synchronous power source fault characteristics may misjudge the faults. For example, during low-voltage ride-through, an IIDG may output a current nearly perpendicular to the voltage phase, leading to deviations in the phase comparison results of traditional directional elements. Therefore, this application introduces positive-sequence current amplitude as an auxiliary constraint based on the directional criterion. Through the fusion of multi-dimensional information, it reduces the failure risk of a single criterion under complex operating conditions.

[0137] In step S502, the protection device integrates the direction judgment, positive sequence current amplitude, preset current protection threshold and signal characteristics of the blocking signal from the system side, and performs protection operations according to preset logic rules. The protection operations include at least two types: signal interruption operation and tripping operation.

[0138] The preset current protection threshold can refer to the upper limit current threshold used for protection action judgment, that is, the amplitude boundary used to distinguish between weak feeder fault current and normal load current. Its setting relationship is such that it is greater than the maximum load current of the active distribution network, so that the protection equipment can still identify the positive sequence current amplitude exceeding the threshold as a current characteristic closer to the fault state when load fluctuations, reverse power flow, and non-fault through current exist. For example, the preset current protection threshold can be twice the maximum system load current.

[0139] After detecting a fault, the system-side protection equipment generates a blocking signal based on the direction determination result and the status of the starting elements, and sends it to the weak-feed side protection equipment via a communication link (such as fiber optic, carrier, or wireless communication channel). The blocking signal is a logic level signal or a digitally coded signal; its valid state (such as high level or specific code) indicates "blocking required," and its invalid state (such as low level or idle code) indicates "tripping allowed." The weak-feed side protection equipment receives this signal through a communication interface and monitors its status changes in real time.

[0140] Signal characteristics can refer to the state change pattern of the blocking signal in the time domain, specifically including: whether the signal exists, the duration of the signal, whether the signal changes from an effective state to an invalid state (e.g., the timing characteristic of "existing first and then disappearing"), and the state reversal time of the signal.

[0141] Protection operation can refer to the control of fault response behavior by the weak feeder side protection equipment based on the comprehensive judgment result. Optionally, protection operation can include the following three categories: (1) signal interruption operation, that is, stopping the transmission of blocking signals to the protection equipment on the other side, so that the tripping circuit of the protection equipment on the other side is opened; (2) tripping operation, that is, issuing a tripping command to the circuit breaker to cut off the fault current and realize the isolation of the fault section; (3) maintaining the blocking state, that is, continuing to send blocking signals to the other side without performing tripping, and maintaining the power supply of the line.

[0142] In one possible implementation, step S502 may include the following sub-steps:

[0143] S502a. Based on the direction criterion and the positive sequence current amplitude, determine whether the weak feeder-side protection device meets the preset shutdown conditions. The shutdown conditions include: Condition 1, the direction criterion indicates the fault is in the positive direction (i.e., the local protection starting element operates and the direction element identifies the fault as being in the positive direction); Condition 2, the direction criterion indicates the fault is not in the positive direction, the positive sequence current amplitude is less than the preset current protection threshold, and a blocking signal from the system side is continuously received for a preset duration (e.g., 5 to 7 milliseconds, this duration taking into account communication channel transmission delay and signal processing delay). If either Condition 1 or Condition 2 is met, the shutdown conditions are deemed met, and the protection device is controlled to stop sending blocking signals.

[0144] S502b: Based on the direction criterion, positive sequence current amplitude, preset current protection threshold, and signal characteristics of the blocking signal, determine whether the weak feeder-side protection device meets the preset tripping conditions. The tripping conditions include: Condition 1: The direction criterion indicates the fault is in the positive direction, and no blocking signal is received from the system side (i.e., the other side has stopped communicating); Condition 2: The direction criterion indicates the fault is not in the positive direction, the positive sequence current amplitude is less than the preset current protection threshold, and the signal characteristics of the blocking signal indicate that the signal exhibits a "pre-existence then disappearance" timing change. If either Condition 1 or Condition 2 is met, the tripping condition is deemed met, and the protection device is controlled to perform a tripping operation.

[0145] S502c: When the shutdown condition is not met, the control and protection equipment continuously sends a blocking signal; when the tripping condition is not met, the control and protection equipment remains in the blocking state and does not perform a trip.

[0146] It is understandable that this application fundamentally avoids the technical defect of unclear voltage characteristics caused by high transition resistance by introducing a positive sequence current amplitude criterion to replace the traditional voltage threshold criterion; by introducing the signal characteristics of the blocking signal as a necessary condition for tripping, it accurately distinguishes the essential differences between the fault section and the downstream non-fault section in the blocking signal interaction process. Both of the above improvements are based on the quantitative analysis of the steady-state characteristics of weak feeder side faults, and have clear physical basis and engineering feasibility. In addition, while optimizing the protection logic of the weak feeder side, this application retains the basic framework of traditional blocking-type directional longitudinal protection, including mature mechanisms such as start signaling, remote start signaling, system-side stop signaling and tripping, without requiring additional modifications to the communication link, data synchronization method or hardware equipment, and is easy to implement through software upgrades on existing distribution network protection devices.

[0147] This embodiment provides a protection method for active distribution networks. By introducing the positive-sequence current amplitude as the core criterion for weak-feed side protection, replacing the traditional criterion method that relies on voltage thresholds, it avoids the risk of weak-feed side failure to operate due to unclear voltage characteristics under high transition resistance faults. By combining the dual constraints of direction criterion and positive-sequence current amplitude, and introducing the signal characteristics of the blocking signal from the system side as an auxiliary discrimination basis, it distinguishes the differences between the faulty section and the downstream non-faulty section in the signal interaction process, reducing the risk of false operation caused by misjudgment of direction in the non-faulty section. By fusing the positive-sequence current amplitude, direction criterion, and signal characteristics of the blocking signal for decision-making, the weak-feed side protection equipment can still accurately perform protection operations under the complex operating conditions of active distribution networks with weak fault current amplitude and uncertain direction. The method of this application improves the reliability and stability of fault protection in active distribution networks.

[0148] Figure 6 Flowchart of the protection method for active power distribution networks provided in this application Figure 2 , Figure 7 Based on the aforementioned embodiments, the embodiments further illustrate the protection method for active power distribution networks, such as... Figure 6 As shown, the method includes:

[0149] S601. Real-time acquisition of three-phase electrical information; wherein, the three-phase electrical information represents the electrical quantity parameters at the installation location of the protection equipment, and the three-phase electrical information includes three-phase voltage information and three-phase current information.

[0150] The three-phase voltage information refers to the digital quantity obtained by analog-to-digital conversion of the three-phase voltage signals acquired in real time at the installation location of the protection equipment through a voltage transformer or voltage tapping unit. It can include the instantaneous sampled values ​​or fundamental vector values ​​of phase A, phase B, and phase C voltages.

[0151] Three-phase current information refers to the digital quantity obtained by analog-to-digital conversion of the three-phase current signals acquired in real time at the installation location of the protection equipment through current transformers or current collection units. It can include the instantaneous sampled values ​​or fundamental vector values ​​of phase A current, phase B current, and phase C current.

[0152] It should be understood that the three-phase voltage information and the three-phase current information together constitute the basic data source for determining the execution direction of the protection device, and their sampling frequency, synchronization accuracy and filtering processing method should be consistent.

[0153] S602. Filter the three-phase voltage information and the three-phase current information respectively to determine the positive sequence voltage phasor corresponding to the three-phase voltage information and the positive sequence current phasor corresponding to the three-phase current information.

[0154] Filtering refers to the process of digitally filtering a discrete digital sequence after analog-to-digital conversion to extract the fundamental component and suppress high-frequency harmonics, attenuate DC components, interharmonics, and high-frequency noise interference. The purpose of filtering is to improve the extraction accuracy of the fundamental component, ensure the accuracy of subsequent positive-sequence component calculation, and avoid misjudgments caused by harmonic interference or transient components.

[0155] Optionally, the filtering process can employ a finite impulse response (FIR) digital filter, a full-wave Fourier algorithm, or a half-wave Fourier algorithm to eliminate interference from high-frequency harmonics, attenuated DC components, and interharmonics on the extraction of the fundamental component. After filtering, the three-phase voltage fundamental phasors and three-phase current fundamental phasors can be converted into positive-sequence voltage phasors and positive-sequence current phasors using a symmetrical component transformation matrix.

[0156] A positive-sequence voltage phasor can refer to a complex phasor representing the positive-sequence component of a three-phase voltage, obtained after symmetrical component transformation. Its magnitude represents the positive-sequence voltage amplitude, and its phase angle represents the positive-sequence voltage phase. Similarly, a positive-sequence current phasor can refer to a complex phasor representing the positive-sequence component of a three-phase current, obtained after symmetrical component transformation. Its magnitude represents the positive-sequence current amplitude, and its phase angle represents the positive-sequence current phase.

[0157] S603. Determine the positive sequence current amplitude based on the positive sequence current phasor.

[0158] Specifically, the magnitude of the positive sequence current can be determined by the magnitude of the positive sequence current phasor, that is, by taking the square root of the sum of the squares of the real and imaginary parts of the positive sequence current, or directly by the output of the phasor algorithm.

[0159] In one possible implementation, the positive sequence current amplitude can be calculated using a sliding data window method, which updates the calculation results within the data window once for each sampling point to improve response speed and real-time performance; or a fixed data window method can be used, which calculates the results once for each power frequency cycle to improve calculation stability and anti-interference capability.

[0160] S604. Determine the direction criterion based on the positive sequence voltage phasor and the positive sequence current phasor.

[0161] In one alternative implementation, step S604 may include:

[0162] S6041. Determine the positive-sequence phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor;

[0163] S6042. If the positive sequence phase difference is within the preset phase range, then the direction criterion characterizing the orientation relationship between the fault point and the protection device is determined to be positive.

[0164] The positive sequence phase difference can refer to the difference in phase angle between the positive sequence voltage phasor and the positive sequence current phasor. For example, the positive sequence voltage phasor and the positive sequence current phasor can be divided by a complex number and the phase angle part can be extracted as the positive sequence phase difference; or the phase angles of the two phasors can be calculated separately and then the difference can be obtained to obtain the phase relationship between the positive sequence voltage and the positive sequence current, thereby determining the power flow direction and fault location.

[0165] The preset phase interval refers to the allowable range of positive sequence phase difference, pre-set according to the line impedance angle and protection sensitivity requirements, used to determine whether the fault is located in the positive direction. The setting of this phase interval needs to take into account factors such as line type (overhead line or cable), line length, and system operation mode to ensure that the fault direction can be reliably determined under various fault conditions.

[0166] For example, the preset phase range can be [-45°, 135°]. When the positive sequence phase difference is within this range, it indicates that the positive sequence power flows from the bus to the line, and the fault is located in the positive direction of the protection device. When the positive sequence phase difference is outside this range, it indicates that the positive sequence power flows from the line to the bus or the fault point is located in the opposite direction of the protection device, and the fault is determined to be located in the opposite direction of the protection device.

[0167] In one possible implementation, the preset phase range can be set differently according to the different line impedance angles to adapt to the different fault characteristics under different line types and system operating conditions. For example, for overhead lines, the line impedance angle is usually between 60° and 85°. The preset phase interval can be narrowed accordingly to [0°, 90°] or [-15°, 105°] to improve the sensitivity and reliability of direction determination and avoid misjudgment caused by the phase difference being close to the interval boundary when the line impedance angle is large. For cable lines, the line impedance angle is usually between 20° and 45°. The preset phase interval can be widened accordingly to [-60°, 150°] or [-75°, 165°] to cover the small phase difference change range between positive sequence voltage and positive sequence current when cable lines are faulty, ensuring that the fault direction can be reliably determined in cable networks. For mixed lines (overhead lines and cables are installed together), the preset phase interval can adopt a segmented adaptive strategy, that is, dynamically switch the phase interval according to the type of the line segment where the protection is installed, or adopt a compromise interval such as [-30°, 120°] to take into account the fault characteristics of both types of lines.

[0168] In one possible implementation, the direction criterion can also be determined using a positive-sequence power direction criterion as an auxiliary method. Specifically, the product of the positive-sequence voltage phasor and the positive-sequence current phasor can be determined as the positive-sequence complex power. If its real part is greater than 0, it indicates that the positive-sequence active power flows from the bus to the line, thus helping to confirm that the fault is located in the positive direction; otherwise, it is located in the reverse direction. This auxiliary criterion can be used in parallel with the positive-sequence phase difference criterion to improve the reliability of direction determination.

[0169] In another optional implementation, the direction criterion can also be determined in parallel with the negative sequence component. For example, the negative sequence phase difference between the negative sequence voltage phasor and the negative sequence current phasor is calculated and compared with the system's average negative sequence impedance angle. If the absolute value of the difference between the negative sequence phase difference and the system's average negative sequence impedance angle is less than 90°, the negative sequence direction criterion indicates that the fault is located in the positive direction; otherwise, it indicates that the fault is located in the reverse direction. The system's average negative sequence impedance angle can be preset based on the system's negative sequence impedance parameters or estimated through online measurement. Alternatively, for example, the negative sequence phase difference between the negative sequence voltage phasor and the negative sequence current phasor is determined (the steps for determining the negative sequence phase difference between the positive sequence voltage phasor and the positive sequence current phasor are similar and will not be repeated here). If the negative sequence phase difference is within a preset negative sequence phase range (e.g., [-270°, -90°]), the direction criterion indicates that the fault point's orientation relative to the protection device is in the positive direction.

[0170] Specifically, when at least one of the positive-sequence direction criteria and the negative-sequence direction criteria indicates that the fault is located in the positive direction, the direction criterion characterizing the fault point's orientation relative to the protection equipment is determined to be in the positive direction. This parallel discrimination method can adapt to the influence of the IIDG negative-sequence suppression control strategy and improve the reliability of direction discrimination.

[0171] It is understandable that by comparing the positive-sequence phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor to determine the orientation relationship of the direction criterion, the universality of the positive-sequence component in various fault types (including three-phase short circuit, two-phase short circuit, two-phase ground short circuit, etc.) can be fully utilized, avoiding the limitation that the negative-sequence component only appears in asymmetrical faults and the zero-sequence component only appears in ground faults. This improves the applicability and reliability of the direction criterion under different fault types and achieves comprehensive coverage of fault orientation discrimination.

[0172] S605. Determine the positive sequence current amplitude and direction criteria for fault detection information.

[0173] Specifically, the positive sequence current amplitude and direction criteria are combined into fault detection information, which serves as the core input for subsequent protection logic judgment.

[0174] It is understandable that by determining the positive sequence current amplitude based on the positive sequence voltage phasor and the positive sequence current phasor, and by determining the direction criterion by comparing the positive sequence phase difference, as fault detection information, the stability and symmetry of the positive sequence component during the fault steady state can be fully utilized, avoiding interference from high-frequency components and attenuated DC components during the transient process. This improves the accuracy and reliability of fault detection information, provides an effective data foundation for the reliable execution of subsequent signal interruption and tripping operations, and enables the weak feeder protection equipment to accurately identify faults under complex operating conditions.

[0175] S606. Based on the positive sequence current amplitude and the preset current judgment threshold, determine the sending status of the blocking signal to the system side; wherein, the preset current judgment threshold is less than the preset current protection threshold and greater than the maximum load current of the active distribution network.

[0176] The preset current judgment threshold can refer to the lower limit current threshold used to initiate the blocking signal sent by the weak feeder side protection device. For example, the preset current judgment threshold can be set to 1.2 times the maximum load current of the active distribution network.

[0177] Specifically, the selection of this threshold must meet two constraints: first, it must be greater than the maximum load current of the system to avoid normal load fluctuations and transient currents during startup, thus preventing false signaling during normal operation; second, it must be less than the preset current protection threshold to form a two-level threshold system, so that the signaling startup and protection action judgment have a clear logical hierarchy and timing coordination.

[0178] In one possible implementation, the preset current judgment threshold can be adaptively adjusted based on historical load data of the active distribution network, distributed generation output forecasts, and seasonal load changes. For example, during the midday hours in summer when distributed generation penetration is high, the maximum load current may decrease due to photovoltaic power feedback. In this case, the current judgment threshold can be lowered to 1.1 times the maximum load current of the active distribution network. During the evening hours in winter when distributed generation penetration is low, the maximum load current may increase due to increased heating load. In this case, the current judgment threshold can be raised to 1.3 times the maximum load current of the active distribution network to ensure that the threshold is always within a reasonable range, balancing sensitivity and reliability.

[0179] The transmission status refers to the current state of the weak-feed side protection device sending a blocking signal to the system side. It characterizes whether the weak-feed side protection device is currently outputting a blocking signal to the system side and is a fundamental prerequisite for subsequent stop and trip operations. It should be understood that the transmission status directly reflects the degree of communication participation of the weak-feed side protection device in the blocking longitudinal protection. Only when it is in the transmission state does the subsequent stop operation have practical significance.

[0180] In an optional implementation, the transmission status includes a transmission in progress status or a transmission stopped status, and step S606 may include:

[0181] S6061. If the positive sequence current amplitude is greater than the preset current judgment threshold, then the transmission state is determined to be the transmission in progress state.

[0182] S6062. If the positive sequence current amplitude is less than or equal to the current judgment threshold and a blocking signal from the system side is received within the preset communication time window, then the transmission state is determined to be the transmission in progress state.

[0183] S6063. If the positive sequence current amplitude is less than or equal to the current judgment threshold and no blocking signal is received from the system side within the preset communication time window, then the transmission status is determined to be the transmission stop status.

[0184] The "transmission in progress" state refers to the state where the weak-feed side protection device is sending a blocking signal to the system side. In this state, the communication interface of the weak-feed side protection device is in active transmission mode, continuously outputting a logic level or digital coded signal indicating a "blocking request." Upon receiving this signal, the system-side protection device blocks its tripping circuit. The "transmission stopped" state refers to the state where the weak-feed side protection device is not sending a blocking signal to the system side. In this state, the communication interface of the weak-feed side protection device is in silent or receive mode, not outputting a blocking signal to the system side. The system-side protection device can perform a tripping operation if it does not receive a blocking signal and meets its own tripping conditions. In one possible scenario, the "transmission stopped" state occurs when the fault has not occurred, the fault is located outside the fault zone, or a stop-signal operation has already been performed on the system side.

[0185] The preset communication time window can refer to the waiting time used to determine whether the weak-feed side protection device has received the system-side blocking signal. The setting of this time must take into account both the fluctuation of communication channel transmission delay and the requirements of protection action speed. For example, the preset communication time window can be 5 to 7 milliseconds.

[0186] Specifically, the lower limit of the preset communication time window should be greater than the sum of the maximum one-way transmission delay of the communication channel (typically 2 to 4 milliseconds for fiber optic channels, 4 to 6 milliseconds for carrier channels, and 5 to 10 milliseconds for wireless channels) and the signal processing delay (typically 1 to 2 milliseconds), ensuring that the weak-feed side protection equipment has sufficient time to receive and acknowledge the blocking signal from the system side; the upper limit of the preset communication time window should be less than one-tenth of the overall time limit for the system-side protection from fault detection to trip output (typically 80 to 120 milliseconds), avoiding excessive waiting time that could affect the protection's speed. Therefore, a value range of 5 to 7 milliseconds can cover the delay characteristics of most distribution network communication channels while meeting the protection's speed requirements.

[0187] Specifically, if the positive sequence current amplitude is greater than the preset current judgment threshold, it indicates that a significant fault current characteristic has been detected at the installation location of the weak feeder side protection equipment, and the local fault initiation element has been activated. At this time, the weak feeder side protection equipment should actively participate in the information interaction of the interlocked longitudinal protection, and the sending state is determined to be the sending in progress state. The weak feeder side protection equipment actively sends an interlocking signal to the system side, so that the tripping circuit of the system side protection equipment is interlocked, and the initial coordination of the protection on both sides is achieved.

[0188] If the positive sequence current amplitude is less than or equal to the current judgment threshold and a blocking signal is received from the system side within the preset communication time window, it indicates that the fault current at the weak feeder protection device installation location is weak (possibly due to low distributed power penetration, a distant fault point, or a large transition resistance). The local starting element has not activated, but the system-side protection device has detected the fault and sent a blocking signal. At this time, the weak feeder protection device passively participates in information interaction through remote signaling redundancy logic, and the sending status is determined to be the sending in progress status. After receiving the blocking signal from the system side, the weak feeder protection device forcibly starts its own signaling and replies to the system side with the blocking signal, ensuring the integrity of information interaction between the two protection sides and avoiding coordination failure due to the weak feeder not sending a signal.

[0189] If the positive sequence current amplitude is less than or equal to the current judgment threshold and no blocking signal is received from the system side within the preset communication time window, it indicates that there is no fault at the installation location of the weak feeder side protection device or the fault is located outside the zone. The local starting element does not operate, and the system side protection device also does not detect the fault or send a blocking signal. At this time, both protection devices are in normal operation. Then, the sending state is determined to be the sending stop state. The weak feeder side protection device does not send a blocking signal to the system side to avoid false transmission during normal operation, keep the tripping circuit of the system side protection device open, and ensure normal power supply under non-fault conditions.

[0190] It is understandable that by setting two levels of current thresholds (the current judgment threshold is used to start transmission and the current protection threshold is used to constrain the weak feeder side protection logic) and introducing remote signaling redundancy logic, the specific switching rules of the transmission state can be determined. In scenarios where the fault current on the weak feeder side is weak and the sensitivity of the local starting element is insufficient, the transmission can be forcibly started by relying on the blocking signal on the system side, ensuring the integrity of information interaction between the two protection sides, thereby avoiding the failure of protection coordination caused by the lack of single-sided transmission, and realizing the reliable start of the blocking longitudinal protection under all operating conditions.

[0191] S607. Based on the transmission status, direction criterion, positive sequence current amplitude, preset current protection threshold, and signal characteristics, execute a signal stop operation.

[0192] Among them, the protection operation includes the stop signal operation, which means stopping the transmission of blocking signals to the system side.

[0193] Specifically, the signal interruption operation can refer to the operation of the weak feeder side protection equipment switching from the transmitting state to the transmitting stop state when certain conditions are met, that is, stopping the output of blocking signals to the system side, so that the tripping circuit of the system side protection equipment is opened.

[0194] In an optional implementation, step S607 may include:

[0195] If the transmission status is in progress, the direction criterion indicates that the orientation of the fault point relative to the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the first characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a signal stop operation is performed; wherein, the first characteristic condition indicates that the blocking signal received from the system side has reached the preset signal duration.

[0196] The system-side blocking signal refers to a logic signal generated by the system-side protection equipment and sent to the weak-feed side protection equipment via a communication link. It indicates the system-side protection equipment's judgment result regarding the fault direction or its protection status. When valid, this signal indicates "blocking required," meaning the weak-feed side protection equipment is required to block its tripping circuit; when invalid, it indicates "tripping permitted," meaning the weak-feed side protection equipment is allowed to trip when its own tripping conditions are met.

[0197] The first characteristic condition can refer to the time constraint condition used to confirm the continuous validity of the system-side blocking signal, that is, the weak-feed side protection device continuously and uninterruptedly receives a valid blocking signal from the system side within a preset signal duration. The purpose of setting this condition is twofold: first, to confirm that the system-side protection device has stably entered the transmitting state, rather than experiencing a brief, accidental blocking signal due to transient interference, communication jitter, or electromagnetic noise; and second, to provide the weak-feed side protection device with sufficient signal confirmation time, enabling it to make a reliable shutdown decision based on the stable existence of the system-side blocking signal. For example, the first characteristic condition can be that the weak-feed side protection device continuously and uninterruptedly receives a valid blocking signal from the system side within 5 to 7 milliseconds. This preset signal duration and the preset communication time window can be set to the same or different values. When set to the same value, parameter configuration is simplified, facilitating engineering implementation; when set to different values, a time-level coordination can be formed, allowing the remote signal activation confirmation and continuous reception confirmation to have independent timing constraints, improving the flexibility and reliability of the logic.

[0198] The combination of the above four conditions constitutes the optimized shutdown logic for weak-feed side protection equipment in weak-feed scenarios:

[0199] If the transmission status is in progress, it ensures that the weak feeder protection device has participated in the blocking signal interaction and meets the prerequisite for stopping the transmission; if the transmission is stopped, there is no need to perform the stopping operation.

[0200] If the direction criterion indicates that the orientation relationship between the fault point and the protection equipment is not positive, it means that the directional element on this side has not directly judged it as positive. This may be due to the weak fault current, the influence of the transition resistance, or the distributed power supply control strategy, which may lead to unclear direction discrimination or misjudgment as the opposite direction. In this case, other auxiliary conditions need to be relied upon to make the shutdown decision.

[0201] If the signal characteristics of the blocking signal on the system side meet the first characteristic condition, it indicates that the protection device on the system side has stably sent the blocking signal and has continued for a preset duration (e.g., 5 to 7 milliseconds). This confirms that the system side has detected the fault and entered the signal transmission state. This delayed confirmation mechanism avoids misjudgment caused by instantaneous interference or signal jitter in the communication channel and improves the reliability of signal discrimination.

[0202] If the positive sequence current amplitude is less than the preset current protection threshold, it indicates that this side is in a weak feeder scenario, the fault current is weak, and it is clearly distinguished from the strong short-circuit current on the system side. This condition separates the weak feeder side shutdown logic from the system side standard shutdown logic (direct shutdown when the direction criterion is positive), avoiding confusion and conflict between the two logics.

[0203] When all four conditions are met, the weak-feed side protection equipment performs a signal stop operation, ceasing to send blocking signals to the system side, and cooperates with the system-side protection equipment to complete the isolation of the fault section.

[0204] It is understandable that by comprehensively considering the transmission status (ensuring that the local side is in the transmission process and meets the prerequisite for signal interruption), direction criteria (confirming that the local side is not directly judged as positive, excluding strong fault current scenarios), the comparison result of the positive sequence current amplitude and the current protection threshold (confirming that it is in a weak feeder scenario and the current is weak), and the first characteristic condition of the blocking signal (continuous reception reaches the preset duration, confirming that the system side has stably transmitted), it is determined whether the weak feeder protection device should perform a signal interruption operation. When the fault current on the weak feeder side is weak, the sensitivity of the direction criteria is insufficient, or there is a risk of misjudgment, cross-validation of multi-dimensional information can be used as an auxiliary constraint to ensure the reliability of the signal interruption operation. This avoids premature signal interruption leading to erroneous operation on the other side (if the weak feeder side interrupts the signal prematurely when the system side is not ready to trip, it may lead to misjudgment on the system side) or delayed signal interruption leading to refusal to operate on the local side (the weak feeder side does not interrupt the signal in time, continuously blocking the local side tripping circuit), thus achieving precise control of the weak feeder side signal interruption logic.

[0205] In an optional implementation, step S607 may further include:

[0206] If the transmission status is in progress and the direction criterion indicates that the fault point is in a positive direction relative to the protection device, then a stop-transmission operation is performed.

[0207] This condition applies to scenarios where the fault current on the weak feeder side is strong and the direction criterion clearly indicates a positive direction. In this case, regardless of whether the positive sequence current amplitude is less than the current protection threshold or the signal characteristics of the blocking signal, a shutdown operation is immediately executed. This is because when the direction criterion directly indicates a positive direction, it means the fault is within the protection range of this side, and the weak feeder side should cooperate with the system side to quickly clear the fault without waiting for other conditions to be met. This logic is consistent with the standard shutdown logic of the system side protection, ensuring rapid coordination between the protections on both sides in strong fault current scenarios.

[0208] It is understandable that by supplementing the direction criterion to directly indicate the positive direction, the immediate execution of the stop signal operation can be carried out to determine whether the weak feeder side protection equipment should perform the stop signal operation. This can cover the rapid response requirement of the direction criterion clearly indicating the positive direction in the strong fault current scenario, thereby shortening the fault clearing time, improving the protection speed, and realizing the rapid isolation of the fault section.

[0209] It is understandable that by combining the transmission status of the blocking signal sent to the system side, the orientation relationship of the direction criterion, the comparison result of the positive sequence current amplitude and the current protection threshold, and the first characteristic condition of the blocking signal, a multi-dimensional constraint blocking decision mechanism can be formed to comprehensively execute the blocking operation. This avoids the failure risk of a single criterion under complex operating conditions, thereby improving the reliability and adaptability of the blocking operation and realizing the correct blocking of weak feeder protection under various fault scenarios.

[0210] S608. If the direction criterion indicates that the orientation relationship between the fault point and the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the second characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a trip operation is performed; wherein, the second characteristic condition indicates that a blocking signal is received in the first time period, and no blocking signal is received in the second time period after the first time period.

[0211] Among them, the protection operation includes the tripping operation, which means that the tripping is performed to isolate the faulty section.

[0212] Specifically, a tripping operation refers to the operation whereby the weak-feed side protection equipment sends a tripping command to the local circuit breaker when certain conditions are met, interrupting the fault current and isolating the faulty section. Unlike signal interruption, a tripping operation directly causes a power outage on the line, therefore its execution conditions are more stringent. It is necessary to ensure that the fault is indeed within the protection range of this side to avoid false tripping in non-faulty sections.

[0213] The second characteristic condition can refer to a dynamic discrimination condition used to confirm the unique blocking signal timing pattern of the weak-feeder side protection equipment in the faulty section. Specifically, the weak-feeder side protection equipment continuously receives valid blocking signals from the system side during the first time period, and continuously fails to receive the blocking signal during the second time period after the first time period ends. The purpose of this condition is twofold: first, to accurately identify the faulty section by utilizing the essential timing differences between the faulty section and the downstream non-faulty section during the blocking signal interaction process; and second, to provide a dynamic signal tracking mechanism for the weak-feeder side protection equipment, enabling it to make reliable tripping decisions based on changes in the blocking signal state.

[0214] The combination of the above three conditions constitutes the optimized tripping logic of the weak-feed side protection device in a weak-feed scenario:

[0215] If the orientation criterion indicates that the fault point is not in the positive direction relative to the protection device, it means that the orientation element on this side is not directly judged as the positive direction. This may be due to the weak fault current, the influence of the transition resistance, or the distributed power supply control strategy, which may lead to unclear orientation or misjudgment as the opposite direction. In this case, the timing characteristics of the blocking signal need to be used as an auxiliary judgment basis.

[0216] If the signal characteristics of the blocking signal on the system side satisfy the second characteristic condition, it indicates that the weak-feed side protection equipment has undergone a timing process of "blocking signal first existing and then disappearing," confirming that the system-side protection equipment has first sent the blocking signal and then stopped sending it. That is, the system side has identified it as a positive-direction fault and executed a signal stop operation, and the fault is located in the section between the two protection equipment. This timing characteristic is unique to the weak-feed side protection equipment in the faulty section: the downstream non-faulty section weak-feed side protection equipment continuously receives blocking signals from its system side (i.e., the distributed power source side downstream of the fault point), and there is no "first existing and then disappearing" process, thus it is reliably blocked.

[0217] If the positive sequence current amplitude is less than the preset current protection threshold, it indicates that this side is in a weak feeder scenario, the fault current is weak, and it is clearly distinguished from the strong short-circuit current on the system side. This condition separates the tripping logic on the weak feeder side from the standard tripping logic on the system side (direct tripping when the direction criterion is positive and no blocking signal is received), avoiding confusion and conflict between the two logics.

[0218] When the above three conditions are met simultaneously, the weak feeder side protection equipment performs a trip operation, sends a trip command to the circuit breaker on its side, cuts off the fault current, and cooperates with the system side protection equipment to complete the isolation of the fault section.

[0219] It is understandable that by comprehensively considering the direction criteria (confirming that the current side is not directly judged as positive, excluding strong fault current scenarios), the second characteristic condition of the blocking signal on the system side (experiencing the timing characteristics of "existence followed by disappearance" to accurately identify the unique signal pattern of the fault section), and the comparison result of the positive sequence current amplitude and the current protection threshold (confirming that it is in a weak feeder scenario with a weak current), it can determine whether the weak feeder protection device should perform a trip operation. When the fault current on the weak feeder side is weak, the sensitivity of the direction criteria is insufficient, or there is a risk of misjudgment, the dynamic timing characteristics of the blocking signal can be used as an accurate identifier of the fault section. This contrasts sharply with the pattern of the downstream non-fault section continuously receiving the blocking signal, thereby avoiding the risk of maloperation caused by misjudgment of direction and coincidental fulfillment of the current amplitude conditions in the downstream non-fault section, and achieving reliable differentiation between the fault section and the downstream non-fault section.

[0220] In an optional implementation, the above steps may further include:

[0221] If the direction criterion indicates that the fault point is in a positive direction relative to the protection device, and no blocking signal is received from the system side within the preset communication time window, then a tripping operation is performed.

[0222] This condition applies to scenarios where the fault current on the weak feeder side is strong and the direction criterion clearly indicates a positive direction. In this case, regardless of whether the positive sequence current amplitude is less than the current protection threshold or the signal characteristics of the blocking signal, a tripping operation is immediately performed. This is because when the direction criterion directly indicates a positive direction, it means the fault is within the protection range of this side, and the weak feeder side should cooperate with the system side to quickly clear the fault without waiting for the second characteristic condition to be met. This logic is consistent with the standard tripping logic of the system side protection: when both sides are judged to be in the positive direction and do not send blocking signals to each other, both sides trip simultaneously to achieve rapid isolation of the fault section.

[0223] In one possible implementation, the condition can be extended to: if the direction criterion indicates that the fault point is in a positive direction relative to the protection device, the positive sequence current amplitude is greater than or equal to the preset current protection threshold, and no blocking signal is received from the system side within the preset communication time window, then a tripping operation is performed. This extension further clarifies the boundary between strong fault current scenarios and weak feeder-side scenarios, making the switching between standard tripping logic and optimized tripping logic clearer, and facilitating engineering implementation, debugging, and maintenance.

[0224] It is understandable that by supplementing the direction criteria to directly indicate the positive direction and immediately performing a trip operation when no blocking signal is received, it is possible to determine whether the weak feeder side protection equipment should perform a trip operation. This can cover the fast tripping requirements in strong fault current scenarios where the direction criteria on this side are clear and the signal on the other side has been cut off. This will enable the rapid coordinated action of the protection on both sides, shorten the fault clearing time, and improve the speed of the coordination between the system side and the weak feeder side protection.

[0225] In this embodiment, based on the above embodiments, on the one hand, the positive sequence current amplitude is introduced as the core criterion for weak feeder protection to replace the traditional voltage threshold criterion, so as to solve the problem of weak feeder failure to operate caused by the unclear voltage characteristics under high transition resistance faults; on the other hand, the timing characteristic of the blocking signal "exists first and then disappears" is introduced as a necessary condition for tripping operation, so as to further distinguish the differences between the fault section and the downstream non-fault section in the signal interaction process; thereby achieving the effect of reliable signal shutdown and tripping of the weak feeder protection in the fault section under high transition resistance faults, while achieving the effect of reliable blocking of the weak feeder protection in the downstream non-fault section to avoid maloperation.

[0226] To better illustrate the technical effects of the technical solution in this application, the following provides comparative examples of protection action behaviors under different fault scenarios.

[0227] The following summarizes the composite criteria of "direction criterion + current amplitude + blocking signal timing" used in weak feeder protection to address the problems of weak fault current and uncertain voltage characteristics.

[0228] For the stop signal module: the blocking signal will stop being sent when any of the following conditions are met; otherwise, the blocking signal will continue to be sent.

[0229] Condition 1: Logic element Y1 has an output;

[0230] Condition 2: Three constraints must be met simultaneously: ① No output from Y1 on this side; ② Continuous reception of the blocking signal from the other side for 5 to 7 ms; ③ The positive sequence current amplitude at the protection installation point is less than twice the maximum load current of the system.

[0231] For the trip module: the trip operation is performed when any of the following conditions are met; otherwise, the module remains locked.

[0232] Condition 1: Logic element Y2 has an action output;

[0233] Condition 2: Three constraints must be met simultaneously: ① There is no output from Y1 on this side; ② The received blocking signal from the opposite side exhibits the typical timing characteristic of "the blocking signal first exists and then disappears"; ③ The positive sequence current amplitude at the protection installation point is less than twice the maximum load current of the system.

[0234] Based on the above summary Figure 7 A schematic diagram of the protection operation provided for this application Figure 1 ,exist Figure 7 In the active distribution network shown, the performance of the protection scheme is analyzed when the capacity of the distributed power source downstream of the fault point is large and small. The active distribution network structure is consistent across the analyses.

[0235] Analysis 1:

[0236] For the non-faulty section upstream of the fault point, the short-circuit current flowing through the protection device is relatively large due to the support of the large power supply system, and the directional elements of the protection device can correctly determine the fault location. The transmitting elements of both protection device 1 and protection device 2 are activated, sending blocking signals to their respective sides. Subsequently, protection device 1 satisfies the power supply side stop signaling logic and stops sending blocking signals, while protection device 2 does not satisfy the weak feeder side stop signaling logic and continues to send blocking signals to its own side and the opposite side, thus blocking protection device 1 and itself. Therefore, the protection device in the non-faulty section upstream of the fault point can ensure that no maloperation occurs. The protection operation logic diagram is as follows: Figure 7 As shown.

[0237] The active distribution network includes multiple new energy field sides, power supply sides, load sides, bus A to O (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O), protection devices 1 to 6, and load cells 1 and 2. Starting element 1, denoted as KA1, is a high-sensitivity starting signaling element whose setting value avoids the maximum load current, taking 1.2 times the maximum load current. Starting element 2, denoted as KA2, is a protection starting element whose setting value can be 1.6 to 2 times the signaling element's setting value, taking 2 times the maximum load current. Time elements t1 are the blocking signal delay, typically 100 milliseconds; t2 is the protection trip delay, typically 4 to 8 milliseconds, considering signal transmission delay to prevent false tripping at the remote fault end during external faults. Logic element Y1 outputs when both the protection starting element and the positive direction element operate simultaneously. Logic element Y2 outputs when both the Y1 signal is received and the blocking signal is not received.

[0238] Among them, the interlocking signal can refer to a logic level signal or digitally encoded signal generated by the protection device and transmitted to the protection device on the other side through a communication channel, used to realize the interlocking control of the tripping circuit of the protection device on the other side. Figure 7 In this context, the blocking signal is represented by a dashed line with an arrow, indicating the direction of signal transmission. A valid signal is represented by a high level or a specific code indicating "blocking required," while an invalid signal is represented by a low level or an idle code indicating "tripping allowed." Sending a signal refers to the operation of the protection device sending a blocking signal to the protection device on the other side through its local communication interface. Receiving a signal refers to the operation of the protection device receiving a blocking signal from the protection device on the other side through its local communication interface. The communication channel refers to the physical transmission medium connecting the two protection devices, including fiber optic channels, power line carrier channels, or wireless communication channels, used for bidirectional transmission of the blocking signal. Remote signal initiation refers to the redundant logic where, when the local starting element KA1 has not activated (i.e., the positive sequence current amplitude is ≤ 1.2 times the maximum load current), but a blocking signal is received from the other side within a preset communication time window, the local side forcibly initiates signal transmission to reply with a blocking signal to the other side. A positive direction element can be represented as... The inputs are positive-sequence voltage phasors and positive-sequence current phasors. The fault direction is determined by comparing their phase difference. When the phase difference is within a preset phase range, it is determined to be a positive direction. The negative direction element can be represented as... When the positive direction element does not operate and the negative direction element operates, the auxiliary confirmation indicates that the fault is located in the opposite direction; the falling edge detector is used to identify the "disappearance" moment in the timing characteristic of "blocking signal first exists and then disappears", which, together with the previous "existence" confirmation, constitutes the detection mechanism of the second characteristic condition; the remote signaling implements the functional unit of the remote signaling redundancy logic, including three sub-functions: receiving detection, time window timing, and forced signaling control; the trip command can refer to the action command issued by the protection device to the actuator of the circuit breaker on this side when the tripping condition is met; symbol This represents a logical AND relation, meaning that the AND operation only occurs when the symbol... The output is valid only when all input conditions are met simultaneously; if any input condition is not met, the output is invalid.

[0239] Analysis 2:

[0240] Fault Section. For line BC, when the downstream distributed power supply penetration rate is greater than 100%, the positive sequence current flowing through protection devices 3 and 4 flows from the bus to the line. The short-circuit current provided downstream of the fault point is greater than twice the maximum system load current. Each protection signaling element immediately activates and sends a blocking signal to both its own side and the opposite side. Subsequently, the protection activation and positive direction elements of protection devices 3 and 4 operate, satisfying the stop signal logic and ceasing the transmission of blocking signals. Following this, protection devices 3 and 4 trip because they satisfy the trip logic of logic element Y1 and do not receive a blocking signal, thus clearing the fault. Figure 8 A schematic diagram of the protection operation provided for this application Figure 2 The protection action logic diagram is as follows: Figure 8 As shown.

[0241] When the downstream IIDG capacity is small, the positive sequence current flowing through protection device 3 flows from the bus to the line. Both the transmitting and starting elements of protection device 3 activate, first sending a blocking signal to its local side and protection device 4. For protection device 4, the positive sequence current flowing through it may be from the bus to the line, or from the line to the bus, but the current amplitude is very small. If the current amplitude is greater than 1.2 times the maximum load current, its transmitting element activates and sends a blocking signal to protection device 3 and its local side. Subsequently, the starting element of protection device 3 operates and stops sending the blocking signal, while protection device 4, satisfying the weak feeder side tripping logic, synchronously stops sending the blocking signal. At this time, protection device 3 trips, satisfying the power supply side tripping criterion. Finally, protection device 4, experiencing the blocking signal appearing and disappearing, trips, satisfying the weak feeder side tripping criterion, and the fault is reliably cleared. If the positive sequence current flowing through protection 4 is less than 1.2 times the maximum load current, protection device 3 will inevitably send a signal, and protection 4 can be forced to send a signal through remote signaling logic; the subsequent signaling and tripping process is the same as above, and the fault can still be correctly cleared, ensuring that the protection device has no risk of failure to operate. Figure 9A schematic diagram of the protection operation provided for this application Figure 3 The protection action logic diagram is as follows: Figure 9 As shown.

[0242] Analysis 3:

[0243] Downstream of the fault point, in the non-faulty section. For line CD, the positive sequence current flowing through the protection device is from the distributed power source to the fault point. When the capacity of the distributed power source corresponding to protection device 5 downstream of the fault point is large, the reverse-direction element of protection device 5 operates, continuously sending a blocking signal; the forward-direction element of protection device 6 operates, stopping the sending of the blocking signal. At this time, the protection device reliably blocks, with no risk of misjudgment. Figure 10 A schematic diagram of the protection operation provided for this application Figure 4 The protection action logic diagram is as follows: Figure 10 As shown.

[0244] When the distributed power supply capacity corresponding to protection device 4 is larger than that corresponding to protection device 5, the reverse component of protection device 5 will operate and continuously send a blocking signal. Although protection device 6 can stop sending signals because it meets the weak feeder side stop signaling logic, the tripping criterion of protection device 6 cannot be met because protection device 5 continues to send blocking signals to it. Therefore, the protection device remains blocked to avoid false tripping. Figure 11 A schematic diagram of the protection operation provided for this application Figure 5 The protection action logic diagram is as follows: Figure 11 As shown.

[0245] When the capacity of the distributed power source downstream of the fault point is small, if the amplitude of the positive sequence current flowing through the protection is less than 1.2 times the maximum load current of the system, neither the protection's transmitting element nor the starting element will operate, forming an effective area isolation. If the amplitude of the positive sequence current flowing through the protection is between 1.2 and 2 times the maximum load current: if the transmitting elements of both protection device 5 and protection device 6 operate and transmit normally, protection device 6 can stop transmitting if it meets the weak feeder side stop signaling logic. However, because the logic element Y1 of protection device 5 does not operate, it continues to send a blocking signal to its own side and protection device 6. The protection device is reliably blocked, and there is no false judgment of operation. If only the transmitting element of protection device 5 operates, protection device 6 can force transmission through remote start signaling logic. The subsequent stop signaling and tripping process is the same as above, and the protection device can still reliably block, avoiding false operation. Figure 12 A schematic diagram of the protection operation provided for this application Figure 6 The protection action logic diagram is as follows: Figure 12 As shown.

[0246] When a transition resistance exists at the fault point, the upstream current flowing downstream increases, leading to a decrease in the amplitude of the positive-sequence current flowing through the protection device downstream. If the downstream IIDG capacity is extremely small, the positive-sequence current flowing through protection device 4 may exhibit characteristics of line-to-bus flow, posing a risk of directional misjudgment. However, in this case, the current amplitude is extremely small, and the protection starting element will not activate, thus mitigating the risk of directional misjudgment. Therefore, the proposed solution has good adaptability to transition resistance.

[0247] In summary, the proposed optimization strategy effectively avoids the risks of maloperation and failure to operate of the protection device by integrating the positive sequence current amplitude and the dynamic sensing of the blocking signal, and ensures accurate detection and isolation of the fault section.

[0248] Figure 13 This is a schematic diagram of the structure of the protection device for an active distribution network provided in this application. The active distribution network includes a weak feeder side and a system side. This device is applied to the protection equipment on the weak feeder side, such as... Figure 13 As shown, the protection device 130 of the active power distribution network includes: a data acquisition module 1301 and an execution module 1302.

[0249] The acquisition module 1301 is used to acquire three-phase electrical information in real time and determine fault detection information based on the three-phase electrical information. The three-phase electrical information represents the electrical quantity parameters at the installation location of the protection equipment, and the fault detection information includes the positive sequence current amplitude and direction criterion. The direction criterion represents the orientation relationship between the fault point and the protection equipment.

[0250] The execution module 1302 is used to perform protection operations based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side. The blocking signal is used to block the tripping circuit of the protection device, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation is used to control the response behavior of the protection device on the weak feeder side to the fault of the active distribution network.

[0251] In an optional example, the three-phase electrical information includes three-phase voltage information and three-phase current information. The acquisition module 1301 is also used for:

[0252] The three-phase voltage information and three-phase current information are filtered separately to determine the positive sequence voltage phasor corresponding to the three-phase voltage information and the positive sequence current phasor corresponding to the three-phase current information.

[0253] Determine the positive sequence current amplitude based on the positive sequence current phasor;

[0254] The direction criterion is determined based on the positive sequence voltage phasor and the positive sequence current phasor.

[0255] Determine the positive sequence current amplitude and direction criteria to provide fault detection information.

[0256] In an optional example, the acquisition module 1301 is also used for:

[0257] Determine the positive-sequence phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor;

[0258] If the positive sequence phase difference is within the preset phase range, then the direction criterion characterizes the orientation relationship between the fault point and the protection device as the positive direction.

[0259] In an optional example, the protection operation includes a stop signaling operation, which indicates that the blocking signal is stopped from being sent to the system side; the execution module 1302 is used to:

[0260] Based on the positive sequence current amplitude and the preset current judgment threshold, the sending status of the blocking signal to the system side is determined; wherein, the preset current judgment threshold is less than the preset current protection threshold and greater than the maximum load current of the active distribution network.

[0261] Based on the transmission status, direction criteria, positive sequence current amplitude, preset current protection threshold, and signal characteristics, a signal stop operation is executed.

[0262] In an optional example, the sending status includes a sending in progress status or a sending stopped status; execution module 1302 is also used for:

[0263] If the positive sequence current amplitude is greater than the preset current judgment threshold, the transmission state is determined to be in progress.

[0264] If the positive sequence current amplitude is less than or equal to the current judgment threshold and a blocking signal is received from the system side within the preset communication time window, then the transmission state is determined to be the transmission in progress state.

[0265] If the positive sequence current amplitude is less than or equal to the current judgment threshold, and no blocking signal is received from the system side within the preset communication time window, then the transmission status is determined to be the transmission stop status.

[0266] In an optional example, execution module 1302 is also used for:

[0267] If the transmission status is in progress, the direction criterion indicates that the orientation of the fault point relative to the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the first characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a signal stop operation is performed; wherein, the first characteristic condition indicates that the blocking signal received from the system side has reached the preset signal duration.

[0268] In an optional example, execution module 1302 is also used for:

[0269] If the transmission status is in progress and the direction criterion indicates that the fault point is in a positive direction relative to the protection device, then a stop-transmission operation is performed.

[0270] In an optional example, performing a protection operation includes a tripping operation, which characterizes the execution of a trip to isolate a faulty section; the execution module 1302 is also used for:

[0271] If the direction criterion indicates that the orientation relationship between the fault point and the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the second characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then a trip operation is performed; wherein, the second characteristic condition indicates that a blocking signal is received in the first time period and no blocking signal is received in the second time period after the first time period.

[0272] In an optional example, execution module 1302 is also used for:

[0273] If the direction criterion indicates that the fault point is in a positive direction relative to the protection device, and no blocking signal is received from the system side within the preset communication time window, then a tripping operation is performed.

[0274] The protection device for the active power distribution network in this embodiment can execute the technical solution in the above method. Its specific implementation process and technical principle are the same, and will not be repeated here.

[0275] Figure 14 A schematic diagram of the structure of the electronic device provided in this application, such as... Figure 14 As shown, the electronic device 140 provided in this embodiment includes at least one processor 1401 and a memory 1402. Optionally, the electronic device 140 also includes a communication component 1403. The processor 1401, the memory 1402, and the communication component 1403 are connected via a bus 1404.

[0276] In a specific implementation, at least one processor 1401 executes computer execution instructions stored in memory 1402, causing at least one processor 1401 to perform the above-described method.

[0277] The specific implementation process of processor 1401 can be found in the above method embodiment, and its implementation principle and technical effect are similar, so it will not be repeated here.

[0278] In the above embodiments, it should be understood that the processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor.

[0279] The memory may include random access memory (RAM) and may also include non-volatile memory (NVM), such as at least one disk storage device.

[0280] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of illustration, the buses shown in the accompanying drawings are not limited to a single bus or a single type of bus.

[0281] This application also provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the above-described method.

[0282] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0283] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as magnetic disks or optical disks.

[0284] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A protection method for an active power distribution network, characterized in that, The active distribution network includes a weak feeder side and a system side. The method is applied to the protection equipment on the weak feeder side, and the method includes: Real-time acquisition of three-phase electrical information, and determination of fault detection information based on the three-phase electrical information; wherein, the three-phase electrical information represents the electrical quantity parameters at the installation location of the protection equipment, and the fault detection information includes the positive sequence current amplitude and direction criterion, and the direction criterion represents the orientation relationship of the fault point relative to the protection equipment; Based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side, a protection operation is performed; wherein, the blocking signal is used to block the tripping circuit of the protection device, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation is used to control the response behavior of the protection device on the weak feeder side to the fault of the active distribution network.

2. The method according to claim 1, characterized in that, The three-phase electrical information includes three-phase voltage information and three-phase current information; determining fault detection information based on the three-phase electrical information includes: The three-phase voltage information and the three-phase current information are filtered respectively to determine the positive sequence voltage phasor corresponding to the three-phase voltage information and the positive sequence current phasor corresponding to the three-phase current information; The positive sequence current amplitude is determined based on the positive sequence current phasor. The direction criterion is determined based on the positive sequence voltage phasor and the positive sequence current phasor; The positive sequence current amplitude and the direction criterion are determined as the fault detection information.

3. The method according to claim 2, characterized in that, The step of determining the direction criterion based on the positive-sequence voltage phasor and the positive-sequence current phasor includes: Determine the positive-sequence phase difference between the positive-sequence voltage phasor and the positive-sequence current phasor; If the positive sequence phase difference is within a preset phase range, then the direction criterion characterizing the orientation relationship between the fault point and the protection device is determined to be positive.

4. The method according to any one of claims 1-3, characterized in that, The protection operation includes a stop signaling operation, which indicates that the blocking signal is stopped being sent to the system side; the protection operation is performed based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side, including: Based on the positive sequence current amplitude and the preset current judgment threshold, the transmission status of sending the blocking signal to the system side is determined; wherein, the preset current judgment threshold is less than the preset current protection threshold and greater than the maximum load current of the active distribution network. The signal interruption operation is executed based on the transmission status, the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics.

5. The method according to claim 4, characterized in that, The transmission status includes a transmission in progress status or a transmission stopped status; determining the transmission status of sending a blocking signal to the system side based on the positive sequence current amplitude and a preset current judgment threshold includes: If the positive sequence current amplitude is greater than the preset current judgment threshold, then the transmission state is determined to be the transmission in progress state; If the positive sequence current amplitude is less than or equal to the current judgment threshold, and a blocking signal is received from the system side within a preset communication time window, then the transmission state is determined to be the transmission in progress state. If the positive sequence current amplitude is less than or equal to the current judgment threshold, and no blocking signal is received from the system side within the preset communication time window, then the transmission state is determined to be the transmission stop state.

6. The method according to claim 5, characterized in that, The step of executing the signal termination operation based on the transmission status, the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics includes: If the transmission state is the transmission in progress state, the direction criterion indicates that the orientation relationship between the fault point and the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the first characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then the signal stop operation is performed; wherein, the first characteristic condition indicates that the blocking signal received from the system side has reached the preset signal duration.

7. The method according to claim 6, characterized in that, Also includes: If the sending status is the sending in progress state and the direction criterion indicates that the fault point is in a positive direction relative to the protection device, then the signal stop operation is executed.

8. The method according to any one of claims 1-3, characterized in that, The protection operation includes a tripping operation, which represents the execution of a trip to isolate a faulty section; the protection operation is performed based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side, including: If the direction criterion indicates that the orientation relationship between the fault point and the protection device is not positive, the signal characteristics of the blocking signal on the system side meet the second characteristic condition, and the positive sequence current amplitude is less than the preset current protection threshold, then the tripping operation is performed; wherein, the second characteristic condition indicates that the blocking signal is received within the first time period and the blocking signal is not received within the second time period after the first time period.

9. The method according to claim 8, characterized in that, Also includes: If the direction criterion indicates that the fault point is in a positive direction relative to the protection device, and no blocking signal is received from the system side within the preset communication time window, then the tripping operation is performed.

10. A protection device for an active power distribution network, characterized in that, The active power distribution network includes a weak feeder side and a system side. The device is applied to the protection equipment on the weak feeder side, and the device includes: The acquisition module is used to acquire three-phase electrical information in real time and determine fault detection information based on the three-phase electrical information; wherein, the three-phase electrical information represents the electrical quantity parameters at the installation location of the protection device, and the fault detection information includes the positive sequence current amplitude and direction criterion, and the direction criterion represents the orientation relationship between the fault point and the protection device; The execution module is used to perform protection operations based on the direction criterion, the positive sequence current amplitude, the preset current protection threshold, and the signal characteristics of the blocking signal from the system side; wherein, the blocking signal is used to block the tripping circuit of the protection device, the preset current protection threshold is greater than the maximum load current of the active distribution network, and the protection operation is used to control the response behavior of the protection device on the weak feeder side to the fault of the active distribution network.

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