Three-phase short-circuit fault direction identification method, device and equipment for active power distribution network

Abstract

The invention provides a three-phase short-circuit fault direction identification method, device and equipment for an active power distribution network, and relates to the technical field of power system protection and control. The method comprises the steps of obtaining a power grid topology and distributed power supply parameters of an active power distribution network, and calculating the maximum positive sequence fault current amplitude of each distributed power supply in the active power distribution network based on the distributed power supply parameters; for each section switch configured with a feeder terminal in the active power distribution network, the maximum positive sequence short-circuit current amplitude flowing through the section switch when a three-phase short-circuit fault occurs at the upstream of the section switch and the maximum positive sequence short-circuit current amplitude flowing through the section switch when a three-phase short-circuit fault occurs at the downstream of the section switch are calculated based on the power grid topology and the maximum positive sequence fault current amplitude. A minimum positive sequence short circuit current amplitude flowing through the section switch; and based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude, respectively determining three-phase short-circuit fault directions corresponding to the section switches in the active power distribution network. According to the invention, the direction identification accuracy of the three-phase short-circuit fault in the active power distribution network can be improved.

Description

Technical Field

[0001] This invention relates to the field of power system protection and control technology, and in particular to a method, device and equipment for identifying the direction of three-phase short-circuit faults in an active distribution network. Background Technology

[0002] With the increasing proportion of distributed power sources connected, the distribution network has transformed from a single-ended, radial, passive distribution network to an active distribution network with a high proportion of inverter-type distributed power sources connected at multiple points via T-connections. This has fundamentally changed the fault characteristics of the distribution network, posing a severe challenge to power system protection and control methods.

[0003] In the power system protection and control system, quickly and accurately identifying the direction of a three-phase short-circuit fault is the prerequisite and cornerstone for achieving selective tripping, precise isolation of faulty sections, and rapid restoration of power supply to non-faulty areas. Correct short-circuit fault direction determination ensures that protection devices only disconnect faulty components, minimizing the power outage area and guaranteeing the overall reliability and stability of the power grid.

[0004] In traditional single-ended power supply radial passive distribution networks, the direction of short-circuit faults is usually determined by comparing the phase current with the setting value. If the current at the switch with the feeder terminal is greater than the overcurrent protection setting value, the three-phase short-circuit fault is considered to be located in the downstream line (i.e., the forward direction fault); otherwise, it is considered to be the reverse direction fault or no fault.

[0005] However, the applicant's research has revealed that when a three-phase short-circuit fault occurs in an active distribution network, distributed generation systems with fault ride-through capabilities will provide fault current during the fault ride-through period, leading to complex external drain and amplification effects in the distribution of fault current across the entire network. This causes the magnitude of the fault current flowing through the same switch to no longer solely reflect the upstream and downstream location relationship of the short-circuit fault point. Specifically, during a downstream short-circuit fault, the current may decrease due to the external drain effect, causing protection to fail to operate and the short-circuit fault to be unable to be cleared in a timely manner; conversely, during an upstream short-circuit fault, the current may increase due to the amplification effect, causing protection to maloperate and resulting in unnecessary power outages in non-faulty sections.

[0006] In summary, traditional short-circuit fault direction identification methods are not applicable to active distribution networks, resulting in low identification accuracy during the short-circuit fault direction identification process in active distribution networks. Summary of the Invention

[0007] This invention provides a method, apparatus, and equipment for identifying the direction of three-phase short-circuit faults in active distribution networks, which solves the problem of low accuracy in identifying the direction of three-phase short-circuit faults in active distribution networks.

[0008] In a first aspect, embodiments of the present invention provide a method for identifying the direction of a three-phase short-circuit fault in an active distribution network, comprising: Obtain the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters. For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, calculate the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch, and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch. Based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude, the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network is determined respectively.

[0009] Optionally, for each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch is calculated, including: For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology, each distributed power source located downstream of the sectionalizing switch is determined. The maximum positive sequence fault current amplitude of each distributed power source located downstream of the sectionalizing switch is accumulated, and the accumulated result is determined as the maximum positive sequence short-circuit current amplitude.

[0010] Optionally, for each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch is calculated, including: For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology, each distributed power source upstream of the sectionalizing switch and each distributed power source downstream of the sectionalizing switch are determined respectively. For each distributed power source located upstream of the sectionalizing switch, determine the upstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the upstream line impedance coefficient, determine the upstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. For each distributed power source located downstream of the sectionalizing switch, the downstream line impedance coefficient corresponding to each distributed power source is determined, and based on the maximum positive sequence fault current amplitude of each distributed power source and the downstream line impedance coefficient, the downstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch is determined. Determine the reference positive sequence short-circuit current amplitude in the active distribution network; the reference positive sequence short-circuit current is used to reflect the minimum positive sequence short-circuit current amplitude when there is no distributed power source connected to the active distribution network; Calculate the difference between the reference positive sequence short-circuit current amplitude and the positive sequence current amplitudes of each upstream shunt and each downstream shunt, and determine the difference as the minimum positive sequence short-circuit current amplitude.

[0011] Optionally, determining the reference positive-sequence short-circuit current amplitude in the active distribution network includes: Obtain the system-side power supply equivalent voltage, system-side equivalent positive sequence internal impedance, equivalent impedance of each line, and equivalent positive sequence impedance under the minimum operating mode of the system in the active distribution network. Calculate the sum of the equivalent positive sequence internal impedance of the system side, the equivalent impedance of each line, and the equivalent positive sequence impedance under the minimum operating mode of the system, and determine the sum as the total equivalent positive sequence impedance of the line; The current amplitude is calculated based on the equivalent voltage of the system-side power supply and the equivalent positive-sequence total impedance of the line, and the current amplitude is determined as the reference positive-sequence short-circuit current amplitude.

[0012] Optionally, determining the direction of the three-phase short-circuit fault corresponding to each sectionalizing switch in the active distribution network based on the maximum positive-sequence short-circuit current amplitude and the minimum positive-sequence short-circuit current amplitude includes: For each sectionalizing switch equipped with a feeder terminal, the short-circuit setting threshold corresponding to the sectionalizing switch is determined based on the maximum positive sequence short-circuit current amplitude. The short-circuit setting threshold is verified based on the minimum positive sequence short-circuit circuit amplitude. If the verification result of the short-circuit setting threshold is qualified, the positive sequence current amplitude of the sectionalizing switch is obtained, and the direction of the three-phase short-circuit fault corresponding to the sectionalizing switch is determined based on the positive sequence current amplitude and the short-circuit setting threshold.

[0013] Optionally, for each sectionalizing switch equipped with a feeder terminal, based on the positive sequence current amplitude and the short-circuit setting threshold, the direction of the three-phase short-circuit fault corresponding to the sectionalizing switch is determined, including: For each sectionalizing switch equipped with a feeder terminal, if the positive sequence current amplitude is greater than or equal to the short-circuit setting threshold, then it is determined that the three-phase short-circuit fault is located downstream of the sectionalizing switch. If the positive sequence current amplitude is less than the short-circuit setting threshold, then the three-phase short-circuit fault is determined to be located upstream of the sectionalizing switch.

[0014] Optionally, the step of verifying the short-circuit setting threshold based on the minimum positive-sequence short-circuit circuit amplitude includes: Calculate the ratio of the minimum positive sequence short-circuit current amplitude to the short-circuit setting threshold. If the ratio is greater than a preset sensitivity coefficient, then the verification result of the short-circuit setting threshold is determined to be qualified.

[0015] Optionally, for each sectionalizing switch configured with a feeder terminal, a short-circuit setting threshold corresponding to the sectionalizing switch is determined based on the maximum positive-sequence short-circuit current amplitude, including: For each sectionalizing switch equipped with a feeder terminal, the product of the maximum positive sequence short-circuit current amplitude and the preset reliability coefficient is determined as the short-circuit setting threshold corresponding to that sectionalizing switch.

[0016] Secondly, embodiments of the present invention provide a three-phase short-circuit fault direction identification device for an active power distribution network, comprising: The acquisition module is used to acquire the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters. The calculation module is used to calculate, based on the power grid topology and the maximum positive sequence fault current amplitude, the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch for each sectionalizing switch equipped with a feeder terminal in the active distribution network. The identification module is used to determine the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude.

[0017] Thirdly, embodiments of the present invention provide an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0018] Compared to existing technologies, this invention calculates the maximum and minimum positive-sequence short-circuit currents of each sectionalizing switch under a three-phase short-circuit fault scenario by using the power grid topology and the maximum positive-sequence fault current of each distributed power source. This allows for the determination of the current boundaries that each sectionalizing switch may experience under the most severe scenario (the upstream three-phase short-circuit fault is the most severe, and the downstream three-phase short-circuit fault is the least severe) while considering the external drain and boosting effects of the fault currents of each distributed power source. This accurately characterizes the possible current variation range of each sectionalizing switch when three-phase short-circuit faults occur upstream and downstream, overcoming the influence of distributed power sources on the identification of the direction of three-phase short-circuit faults, and thus achieving accurate identification of the direction of three-phase short-circuit faults in active distribution networks. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a typical active power distribution network equivalent system provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of the three-phase short-circuit fault direction identification method for active power distribution networks provided in this embodiment of the invention. Figure 3 This is the system positive sequence equivalent circuit diagram provided in the embodiment of the present invention when a three-phase short circuit fault occurs at the end of section Line2; Figure 4 This is the system positive sequence equivalent circuit diagram provided in an embodiment of the present invention when a three-phase short circuit fault occurs at the end of section Line4; Figure 5 This is a schematic diagram of the fault location in a typical active distribution network equivalent system in the simulation example provided by the embodiments of the present invention; Figure 6 This is a schematic diagram of the structure of the three-phase short-circuit fault direction identification device for active power distribution network provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] When a three-phase short-circuit fault occurs in an active distribution network, distributed generation sources with low-voltage fault ride-through capability will provide fault current during the low-voltage fault ride-through period, resulting in complex external drain and amplification effects in the fault current distribution across the entire network. Here, we provide a brief introduction to the external drain and amplification effects: The external drain effect refers to the phenomenon where, when a fault point is located downstream of a distributed generation source, the fault current output by the distributed generation source will divert or "pump away" a portion of the current that originally flowed upstream through the sectionalizing switches (i.e., protection installation points) equipped with feeder terminals to the fault point, resulting in a reduction in the current flowing through the sectionalizing switches. Here, each sectionalizing switch equipped with a feeder terminal can be considered a protection installation point.

[0022] by Figure 1 Taking the typical active distribution network equivalent system shown as an example, it is assumed that a three-phase short-circuit fault occurs on Line 4 downstream of the sectionalizing switch F3, which is equipped with a feeder terminal. After the fault occurs, the system-side power supply provides the fault current I. SYS The current flows through F3 towards the fault point. Simultaneously, the distributed power source DG4, located upstream of the fault point, detects a voltage drop at the grid connection point, initiates low-voltage fault ride-through, and outputs a fault current I. DG4 It flows towards the fault point. From the perspective of the fault point, it simultaneously draws current from two paths: one is the I flowing from the distant system side via F3. SYS The other path is the I provided by DG4. DG4This reduces the current demand that the fault point draws from the system side. Ultimately, the current flowing through F3 is less than the current without DG4. This is the external drawdown effect, where DG4 draws a portion of the system-side current from the fault point. The external drawdown effect may cause the current amplitude flowing through F3 to be too small during downstream faults, failing to reach the setting value of traditional overcurrent protection, thus causing the protection to fail to operate.

[0023] In this embodiment of the invention, the system side is taken as the power source and the direction of current outflow from the system side is taken as the positive direction, thereby distinguishing the relative upstream and downstream positions of each component in the active distribution network, as well as the direction of the three-phase short-circuit fault.

[0024] The synergistic effect refers to the phenomenon where, when the fault point is upstream of a distributed generation source, the fault current output by the distributed generation source flows through the sectionalizing switch and is injected into the fault point, resulting in an increase in the total current flowing through the sectionalizing switch. Similarly, using... Figure 1 For example, assuming the short-circuit fault occurs on Line 2 upstream of F3, the fault current I supplied by the system side... SYS At the fault point, current is shunted, and it's highly likely that it won't flow through F3 (or the current flowing through F3 will be very small). At this time, DG4, located downstream of the fault point, also detects a voltage drop at the grid connection point and outputs a fault current I. DG4 The current I output by DG4 DG4 The current first flows through switch F3, then upstream to the fault point. Ultimately, the current flowing through F3 is approximately equal to the fault current I supplied by DG4. DG4 This current value is highly likely to be significantly greater than the negligible current (or even zero) flowing through F3 under a three-phase short-circuit fault without DG4. This is the amplification effect, where the current from DG4 helps increase the current flowing through F3. This amplification effect may cause an abnormally large increase in the current amplitude flowing through F3 during an upstream fault, exceeding the setting value of traditional overcurrent protection, leading to maloperation and incorrectly disconnecting downstream fault-free lines.

[0025] In traditional passive distribution networks, fault current is supplied solely by the system side, and its amplitude monotonically decreases with increasing distance from the fault point. Therefore, a fixed current threshold (i.e., the setting value of traditional overcurrent protection) can reliably distinguish the direction of the fault. However, in active distribution networks, due to the external drawdown and amplification effects of distributed generation, the aforementioned setting value of traditional overcurrent protection cannot accurately identify the direction of a three-phase short-circuit fault.

[0026] To accurately identify the direction of a three-phase short-circuit fault in an active distribution network, this invention calculates the maximum and minimum positive-sequence short-circuit currents corresponding to each sectionalizing switch under a three-phase short-circuit fault scenario by using the grid topology and the maximum positive-sequence fault current of each distributed power source. This allows for the determination of the short-circuit current boundaries that each sectionalizing switch may experience under the most severe scenario (most severe upstream short-circuit fault, least severe downstream short-circuit fault) while considering the external drawdown and amplification effects of the fault currents of each distributed power source. This accurately characterizes the possible current variation range of each sectionalizing switch when three-phase short-circuit faults occur upstream and downstream, overcoming the influence of the fault current of distributed power sources on the identification of the direction of the three-phase short-circuit fault, and thus achieving accurate identification of the direction of the three-phase short-circuit fault.

[0027] Figure 1 middle, This represents the voltage source voltage on the high-voltage side of the main branch transformer in an active distribution network, which is equivalent to the voltage source voltage on the low-voltage side, i.e., the equivalent power supply voltage on the system side. This represents the equivalent positive sequence impedance of the high-voltage side system of the main branch transformer to the low-voltage side, and its value is related to the system operating mode. This represents the positive-sequence internal impedance equivalent to the low-voltage side of the transformer, i.e., the positive-sequence internal impedance on the system side. , , , , , , , , , , and These represent the equivalent impedance of each line segment. , , and These represent the equivalent positive-sequence internal impedances of each distribution transformer to the high-voltage side. F1, F2, F3, and F4 are sectionalizing switches with feeder terminals on each main branch. Q1, Q2, Q3, and Q4 represent branch switches with feeder terminals at the outlets of each branch line. Here, the feeder terminal, also known as a feeder terminal unit (FTU), is a core component of the distribution automation system. It can collect real-time electrical quantities such as current and voltage of the line and combine them with status information such as switch positions to achieve real-time monitoring of feeder operation status, fault detection and location, and remote control (such as opening and closing operations). L1 is the tie terminal, which is in the open state during normal system operation.

[0028] The following is combined Figure 2 The method for identifying the direction of a three-phase short-circuit fault in an active distribution network provided in this embodiment of the invention is described in detail below: Step 201: Obtain the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters.

[0029] When a three-phase short-circuit fault occurs in an active distribution network, the grid connection point voltage of each distributed generation within the network begins to drop. When the degree of voltage drop at the grid connection point is within the allowable range for low-voltage fault crossing, the distributed generation will output a fault current corresponding to the depth of the voltage drop at the grid connection point. Here, the maximum fault current that the distributed generation can output is typically 1.2 times its rated current.

[0030] Here, the distributed power source parameters may include the rated power and rated voltage of each distributed power source. In this embodiment of the invention, the rated current can be calculated based on the rated power and rated voltage of each distributed power source, thereby determining the maximum positive-sequence fault current amplitude. Here, the maximum positive-sequence fault current amplitude is the amplitude of the positive-sequence component of the maximum fault current.

[0031] The maximum positive sequence fault current amplitude can be: .

[0032] in, Indicates the first The maximum positive-sequence fault current amplitude of a distributed power source. Indicates the first The rated power of a distributed power source, This indicates the rated voltage at the grid connection point of the distributed power source.

[0033] Step 202: For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the grid topology and the maximum positive sequence fault current amplitude, calculate the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch, and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch.

[0034] For each sectionalizing switch, when a three-phase short-circuit fault occurs upstream of the sectionalizing switch, the amplifying effect of the distributed power sources downstream of the switch will increase the current flowing through the sectionalizing switch. Therefore, this embodiment of the invention determines the maximum positive-sequence short-circuit current amplitude flowing through the sectionalizing switch under the amplifying effect of the distributed power sources, based on the power grid topology and the maximum positive-sequence fault current amplitude of each distributed power source.

[0035] When a three-phase short-circuit fault occurs downstream of the sectionalizing switch, the external drain effect of each distributed power source located upstream and downstream of the sectionalizing switch will reduce the magnitude of the current flowing through the sectionalizing switch. Therefore, in this embodiment of the invention, the minimum positive-sequence short-circuit current amplitude flowing through the sectionalizing switch under the influence of the external drain effect of the distributed power sources is determined according to the power grid topology and the maximum positive-sequence fault current amplitude of each distributed power source.

[0036] By calculating the maximum and minimum positive-sequence short-circuit current amplitudes corresponding to each sectionalizing switch, this invention can clearly identify the worst-case scenario of a fault upstream of the sectionalizing switch and the mildest-case scenario of a fault downstream of the sectionalizing switch under the influence of the fault current of the distributed power source. This allows for the targeted setting of the most suitable short-circuit setting threshold for the sectionalizing switch, so that the direction of the three-phase short-circuit fault corresponding to the sectionalizing switch can be accurately identified directly based on the short-circuit setting threshold.

[0037] Step 203: Based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude, determine the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network.

[0038] It is understandable that when a three-phase short-circuit fault occurs upstream of a sectionalizing switch, the current flowing through the sectionalizing switch is usually less than the current flowing through it when a three-phase short-circuit fault occurs downstream. In other words, for each sectionalizing switch, its maximum positive-sequence short-circuit current amplitude is usually less than its minimum positive-sequence short-circuit current amplitude. Based on this principle, embodiments of the present invention can use the maximum and minimum positive-sequence short-circuit current amplitudes corresponding to the sectionalizing switch as boundaries to determine the short-circuit setting threshold for that sectionalizing switch.

[0039] When identifying the direction of a three-phase short-circuit fault in each sectionalizing switch, the positive-sequence current amplitude of that sectionalizing switch can be collected. If the positive-sequence current amplitude is greater than or equal to the short-circuit setting threshold, the three-phase short-circuit fault is determined to be located downstream of that sectionalizing switch. If the positive-sequence current amplitude is less than the short-circuit setting threshold, the three-phase short-circuit fault is determined to be located upstream of that sectionalizing switch.

[0040] Compared to existing technologies, this invention calculates the maximum and minimum positive-sequence short-circuit currents of each sectionalizing switch under a three-phase short-circuit fault scenario by using the power grid topology and the maximum positive-sequence fault current of each distributed power source. This allows for the determination of the current boundaries that each sectionalizing switch may experience under the most severe scenario (the upstream three-phase short-circuit fault is the most severe, and the downstream three-phase short-circuit fault is the least severe) while considering the external drawdown and amplification effects of the fault currents of each distributed power source. This accurately characterizes the possible current variation range of each sectionalizing switch when three-phase short-circuit faults occur upstream and downstream, overcoming the influence of the fault current of the distributed power source on the identification of the direction of the three-phase short-circuit fault, and thus achieving accurate identification of the direction of the three-phase short-circuit fault.

[0041] It is important to emphasize that for each sectionalizing switch, when the maximum positive-sequence short-circuit current amplitude corresponding to that sectionalizing switch is significantly smaller than its corresponding minimum positive-sequence short-circuit current amplitude, the short-circuit setting threshold can be determined based on the maximum and minimum positive-sequence short-circuit current amplitudes, thereby determining the direction of the three-phase short-circuit fault. If the prerequisite that the maximum positive-sequence short-circuit current amplitude corresponding to that sectionalizing switch is significantly smaller than its corresponding minimum positive-sequence short-circuit current amplitude is not met, then the method provided in this embodiment of the invention is not applicable.

[0042] This limitation is made because the embodiments of the present invention primarily determine the direction of a three-phase short-circuit fault corresponding to a sectionalizing switch based on the relationship between the positive-sequence current amplitude at the sectionalizing switch and its corresponding short-circuit setting threshold. Specifically, if the positive-sequence current amplitude is greater than or equal to the short-circuit setting threshold, the short-circuit fault is determined to be downstream of the sectionalizing switch. If the positive-sequence current amplitude is less than the short-circuit setting threshold, the short-circuit fault is determined to be upstream of the sectionalizing switch. This necessitates that the short-circuit setting threshold be greater than the maximum positive-sequence short-circuit current amplitude (the worst-case scenario for an upstream fault) and less than the minimum positive-sequence short-circuit current amplitude (the mildest-case scenario for a downstream fault) to effectively distinguish between upstream and downstream faults. If the prerequisite that the maximum positive-sequence short-circuit current amplitude is much smaller than its corresponding minimum positive-sequence short-circuit current amplitude is not met, there may be an overlap between the maximum and minimum positive-sequence short-circuit current amplitudes, making it impossible to determine the short-circuit setting threshold and ultimately failing to effectively distinguish the direction of the three-phase short-circuit fault.

[0043] The following section will elaborate on the specific method for determining the short-circuit setting threshold based on the maximum and minimum positive sequence short-circuit current amplitudes, and then determining the direction of the three-phase short-circuit fault.

[0044] In some embodiments, for each sectionalizing switch equipped with a feeder terminal, a short-circuit setting threshold corresponding to the sectionalizing switch is determined based on the maximum positive-sequence short-circuit current amplitude. Then, the short-circuit setting threshold is verified based on the minimum positive-sequence short-circuit current amplitude. If the verification result of the short-circuit setting threshold is qualified, the positive-sequence current amplitude of the sectionalizing switch is obtained, and the direction of the three-phase short-circuit fault corresponding to the sectionalizing switch is determined based on the positive-sequence current amplitude and the short-circuit setting threshold.

[0045] Here, for each sectionalizing switch equipped with a feeder terminal, the product of the maximum positive sequence short-circuit current amplitude and the preset reliability coefficient is determined as the short-circuit setting threshold corresponding to that sectionalizing switch.

[0046] The formula for calculating the short-circuit setting threshold can be expressed as: ; in, Indicates the first The short-circuit setting threshold corresponding to each sectionalizing switch This represents the preset reliability coefficient. For example, based on experience, the reliability coefficient can be taken as 1.2. Indicates the first The maximum positive sequence short-circuit current amplitude corresponding to each sectionalizing switch.

[0047] As described above, when there is a fault upstream of the sectionalizing switch, the positive sequence current amplitude flowing through the sectionalizing switch is relatively small, while when there is a fault downstream of the sectionalizing switch, the positive sequence current amplitude flowing through the sectionalizing switch is relatively large. To accurately distinguish between upstream and downstream faults (i.e., the direction of a three-phase short-circuit fault), this embodiment of the invention can use the maximum positive sequence short-circuit current amplitude as a benchmark to define the upper limit of the current for upstream faults, avoiding confusion with downstream fault currents.

[0048] The core function of the short-circuit setting threshold is to distinguish between upstream and downstream faults. Therefore, in this embodiment of the invention, a reliability coefficient can be multiplied by the maximum positive sequence current amplitude to avoid uncertainties such as parameter errors and fluctuations in distributed power output, ensuring that the upstream fault current never exceeds the short-circuit setting threshold and avoiding misjudgment.

[0049] The maximum positive-sequence short-circuit current amplitude in this embodiment of the invention is essentially the maximum boost current of the downstream DG calculated for each sectionalizing switch. This means that the short-circuit setting threshold is dynamically calculated based on the real-time access capacity and network topology of the downstream DG at the location of each sectionalizing switch.

[0050] The short-circuit setting threshold calculated using the above setting method can adaptively track changes in the power grid structure (such as DG switching and capacity increases / decreases). Regardless of the downstream DG configuration, this short-circuit setting threshold can ensure that the maximum current that may occur during an upstream fault of the sectionalizing switch (mainly due to the boost from the downstream DG) is included, thereby fundamentally preventing protection maloperation caused by the upstream fault current exceeding the fixed threshold due to the boosting effect.

[0051] Based on the above, the prerequisite for this embodiment of the invention is that when a three-phase short-circuit fault occurs upstream of the sectionalizing switch, the maximum positive-sequence short-circuit current amplitude flowing through the sectionalizing switch is much smaller than the minimum positive-sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream. Therefore, this embodiment of the invention uses the minimum positive-sequence short-circuit current amplitude to verify the above-mentioned short-circuit setting threshold, in order to detect whether the above-mentioned prerequisite is met.

[0052] Specifically, the ratio of the minimum positive sequence short-circuit current amplitude to the short-circuit setting threshold is calculated. If the ratio is greater than the preset sensitivity coefficient, the verification result of the short-circuit setting threshold is deemed qualified, meaning that the current active distribution network meets the above prerequisites and the above short-circuit setting threshold can be used to identify the direction of three-phase short-circuit faults.

[0053] The verification formula can be expressed as: .

[0054] in, Indicates the first The minimum positive sequence short-circuit current amplitude corresponding to each sectionalizing switch. This represents the preset sensitivity coefficient. For example, based on experience, the sensitivity coefficient can be set to 1.25.

[0055] If the ratio is less than or equal to the preset sensitivity coefficient, the verification result of the short-circuit setting threshold is deemed unqualified. This means that the current active distribution network does not meet the above prerequisites and cannot use the short-circuit setting threshold to identify the direction of three-phase short-circuit faults. Other types of direction judgment methods can be used, such as the positive sequence power fault direction judgment method.

[0056] Here, the current network topology of the active distribution network, source-load parameters, and distributed power source access status will all affect the verification results.

[0057] The minimum positive-sequence short-circuit current threshold in this embodiment of the invention is essentially the minimum possible current during a downstream fault, taking into account the drain effect of the downstream DG. The verification essentially verifies whether the minimum downstream fault current is significantly greater than the short-circuit setting threshold.

[0058] This invention utilizes the minimum positive sequence short-circuit current threshold to detect whether the short-circuit setting threshold is within a reliable "safe zone" (i.e., whether there is sufficient margin between the maximum upstream current and the minimum downstream current). If the verification is successful, it proves that in the current active distribution network, the aforementioned short-circuit setting threshold has the ability to reliably distinguish the direction of three-phase short-circuit faults, thereby effectively avoiding protection failure caused by the downstream fault current falling below the threshold due to external suction effects.

[0059] In some embodiments, for each sectionalizing switch equipped with a feeder terminal, if the positive sequence current amplitude is greater than or equal to the short-circuit setting threshold, the three-phase short-circuit fault is determined to be located downstream of the sectionalizing switch, i.e., the direction of the three-phase short-circuit fault is positive. If the positive sequence current amplitude is less than the short-circuit setting threshold, the three-phase short-circuit fault is determined to be located upstream of the sectionalizing switch, i.e., the direction of the three-phase short-circuit fault is negative.

[0060] The above direction criterion can be expressed by the formula: .

[0061] in, Indicates the first The direction of a three-phase short-circuit fault for each sectionalizing switch is indicated by a value of 1 (positive) and 0 (negative). Indicates the first The positive sequence current amplitude of each segmented switch. In this embodiment of the invention, the current outflow direction on the system side is set to the positive direction.

[0062] This invention transforms the complex, topology-dependent fault current distribution characteristics in active distribution networks into a reliable, adaptive binary direction determination problem by dynamically calculating and verifying the dedicated short-circuit setting threshold for each sectional switch. This enables accurate and reliable identification of the direction of three-phase short-circuit faults in environments with a high proportion of distributed power sources, significantly improving the speed, selectivity, and reliability of distribution network protection.

[0063] The calculation methods for the maximum and minimum positive sequence short-circuit current amplitudes will be introduced in detail below.

[0064] In some embodiments, for each sectionalizing switch equipped with a feeder terminal in an active distribution network, based on the grid topology, each distributed power source located downstream of the sectionalizing switch is determined; the maximum positive sequence fault current amplitude of each distributed power source located downstream of the sectionalizing switch is accumulated, and the accumulated result is determined as the maximum positive sequence short-circuit current amplitude.

[0065] For each sectionalizing switch, when a three-phase short-circuit fault is located upstream of the sectionalizing switch, the maximum positive sequence fault current amplitude of each distributed power source located downstream of the sectionalizing switch is determined by the boosting effect, which in turn determines the maximum positive sequence short-circuit current amplitude flowing through that sectionalizing switch.

[0066] The formula for calculating the maximum positive sequence short-circuit current amplitude can be expressed as:

[0067] in, Indicates that it is located at the th A collection of distributed power sources downstream of a segmented switch.

[0068] The following is based on Figure 1 Taking the segmented switch F3 as an example, this paper introduces the derivation process of the formula for the maximum positive sequence short-circuit current amplitude.

[0069] For each sectionalizing switch, if a three-phase short-circuit fault is upstream of that switch, the closer the fault point is to the switch, the greater the amplitude of the positive-sequence fault current flowing through it. In the case of a three-phase short-circuit fault upstream of F3, the positive-sequence fault current amplitude flowing through F3 is largest when the fault occurs at the end of section Line 2. Ignoring the load impedance in the system, we can... Figure 1 Each distributed power source in the system is equivalent to a current source. ,get Figure 3 The system's positive sequence equivalent circuit is shown.

[0070] against Figure 3 The positive-sequence equivalent circuit of the system shown can be used to calculate the positive-sequence short-circuit amplitude flowing through the sectionalizer switch F3: ; The maximum positive sequence short-circuit current amplitude can then be expressed as:

[0071] The calculation method for the maximum positive sequence short-circuit current amplitude corresponding to other sectionalizing switches is similar. It is only necessary to distinguish the relative upstream and downstream positions of the distributed power source and the sectionalizing switch, which will not be elaborated here.

[0072] Based on the calculation example for sectionalizing switch F3, the calculation formula for the maximum positive sequence short-circuit current amplitude corresponding to each sectionalizing switch can be derived: .

[0073] In an active power distribution network, when a three-phase short-circuit fault is located upstream of a sectionalizing switch, the current flowing through the sectionalizing switch is mainly provided by downstream distributed power sources. This invention accumulates the maximum positive-sequence fault current amplitudes of each downstream distributed power source as the maximum positive-sequence short-circuit current amplitude. This accurately identifies and quantifies the true and dominant current source in the upstream fault scenario, ensuring that the subsequently set short-circuit setting threshold truly reflects the maximum current level that may occur during an upstream fault.

[0074] This invention, by summing the maximum possible output of all downstream distributed power sources, conservatively estimates the most severe current increment that the boosting effect might cause. Using this conservative maximum value as the basis for setting the short-circuit setting threshold ensures that the set threshold is sufficient to cover the current flowing through the switch under any upstream fault condition (even if all downstream power sources boost at maximum capacity). This eliminates the risk of maloperation caused by the boosting effect leading to current exceeding the traditional overcurrent protection setting.

[0075] In some embodiments, the calculation process for the minimum positive sequence short-circuit current amplitude is as follows: For each sectionalizing switch equipped with a feeder terminal in an active distribution network, based on the grid topology, each distributed power source upstream of the sectionalizing switch and each distributed power source downstream of the sectionalizing switch are determined respectively. For each distributed power source located upstream of the sectionalizing switch, determine the upstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the upstream line impedance coefficient, determine the upstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. For each distributed power source located downstream of the sectionalizing switch, determine the downstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the downstream line impedance coefficient, determine the downstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. Determine the reference positive sequence short-circuit current amplitude in the active distribution network, calculate the difference between the reference positive sequence short-circuit current amplitude and the positive sequence current amplitudes of each upstream shunt and each downstream shunt, and determine the difference as the minimum positive sequence short-circuit current amplitude.

[0076] For each sectionalizing switch, when a three-phase short-circuit fault is located downstream of that sectionalizing switch, the fault current supplied by the system-side power supply to the fault point flows through that sectionalizing switch. Simultaneously, due to the external suction effect, the fault current supplied by distributed power sources located upstream and downstream of that sectionalizing switch will shunt the fault current supplied by the system side, thereby reducing the fault current flowing through that sectionalizing switch. The shunt strength of the distributed power sources on the sectionalizing switch is affected not only by the amplitude of their maximum positive-sequence fault current but also by the impedance of their upstream and downstream lines.

[0077] For each distributed generation source located upstream of the sectionalizing switch, the product of the upstream line impedance coefficient corresponding to that distributed generation source and the maximum positive-sequence fault current amplitude of that distributed generation source is the positive-sequence current amplitude shunt by that distributed generation source to the sectionalizing switch source. In other words, it is the positive-sequence current amplitude drawn / shunt by that distributed generation source from the sectionalizing switch source.

[0078] For each distributed generation source located downstream of the sectionalizing switch, the product of the downstream line impedance coefficient corresponding to that distributed generation source and the maximum positive-sequence fault current amplitude of that distributed generation source is the positive-sequence current amplitude shunt downstream of the sectionalizing switch source by that distributed generation source. In other words, it is the positive-sequence current amplitude drawn / shunt by the distributed generation source from the sectionalizing switch source.

[0079] Here, the upstream line impedance coefficient corresponding to a distributed generation source refers to the ratio of the equivalent positive-sequence impedance of the upstream line to the equivalent positive-sequence total impedance of the line. The downstream line impedance coefficient corresponding to a distributed generation source refers to the ratio of the equivalent positive-sequence impedance of the downstream line to the equivalent positive-sequence total impedance of the line.

[0080] The upstream line equivalent positive sequence impedance refers to the positive sequence impedance between the system-side power source and the distributed generation source, i.e., the positive sequence impedance upstream of the distributed generation source when a three-phase short-circuit fault occurs at the end of the feeder. The downstream line equivalent positive sequence impedance refers to the positive sequence impedance between the distributed generation source and the end of the feeder, i.e., the positive sequence impedance downstream of the distributed generation source when a three-phase short-circuit fault occurs at the end of the feeder. The total equivalent positive sequence impedance refers to the total equivalent positive sequence impedance between the system-side power source and the end of the feeder, i.e., the total equivalent positive sequence impedance when a three-phase short-circuit fault occurs at the end of the feeder.

[0081] In this embodiment of the invention, the reference positive sequence short-circuit current amplitude provided by the system side is first calculated. Based on this, the external drain effect of upstream and downstream distributed power sources is considered, and the positive sequence current amplitude of upstream and downstream shunts of each distributed power source is deducted, thereby obtaining the minimum positive sequence short-circuit current amplitude flowing through the segment switch.

[0082] Here, the reference positive sequence short-circuit current amplitude is used to reflect the minimum positive sequence short-circuit current amplitude when there is no distributed generation in the active distribution network.

[0083] When a three-phase short-circuit fault occurs downstream of a sectionalizing switch, the farther the fault point is from the sectionalizing switch, the smaller the amplitude of the positive-sequence short-circuit current flowing through that sectionalizing switch. For all sectionalizing switches, when a three-phase short-circuit fault occurs at the end of a feeder in an active distribution network, the amplitude of the positive-sequence short-circuit current flowing through each sectionalizing switch is the smallest.

[0084] In the absence of distributed power source access, when a three-phase short-circuit fault occurs at the end of a feeder in an active distribution network, the reference positive-sequence short-circuit current amplitude can be calculated based on the equivalent voltage of the system-side power source and the equivalent positive-sequence total impedance of the line in the active distribution network.

[0085] Specifically, the calculation logic for the reference positive sequence short-circuit current amplitude is as follows: obtain the equivalent voltage of the system-side power supply, the positive sequence internal impedance of the system side, the equivalent impedance of each line, and the equivalent positive sequence impedance under the minimum operating mode of the system in the active distribution network; calculate the sum of the equivalent positive sequence internal impedance of the system side, the equivalent impedance of each line, and the equivalent positive sequence impedance under the minimum operating mode of the system, and determine the sum as the equivalent positive sequence total impedance of the line; calculate the current amplitude based on the equivalent voltage of the system-side power supply and the equivalent positive sequence total impedance of the line, and determine the current amplitude as the reference positive sequence short-circuit current amplitude.

[0086] Based on the above calculation logic, the formula for calculating the amplitude of the reference positive sequence short-circuit current can be determined as follows:

[0087] in, Indicates the reference positive sequence short-circuit current amplitude. Indicates the equivalent voltage of the system-side power supply. This represents the equivalent positive-sequence total impedance of the line when a fault occurs at the end of the feeder, i.e., the equivalent positive-sequence total impedance of the line mentioned above. It represents the equivalent positive sequence impedance under the minimum operating mode of the system.

[0088] Based on the determined baseline positive-sequence short-circuit current amplitude, the formula for calculating the minimum positive-sequence short-circuit current amplitude can be obtained:

[0089] in, Indicates the first The minimum positive sequence short-circuit current amplitude of each sectionalizing switch Indicates that it is located at the th A collection of distributed power sources upstream of a segmented switch. Indicates the first one located upstream of the sectionalizing switch The upstream line impedance coefficient corresponding to each distributed power source. Indicates the first one located upstream of the sectionalizing switch The impedance coefficient of the downstream line corresponding to each distributed power source.

[0090] The following is still in the format of Figure 1 Taking F3 as an example, this paper introduces the derivation process of the formula for the minimum positive sequence short-circuit current amplitude.

[0091] For each sectionalizing switch, if a three-phase short-circuit fault is located downstream of that sectionalizing switch, the farther the three-phase short-circuit fault point is from that sectionalizing switch, the smaller the amplitude of the positive-sequence fault current flowing through that sectionalizing switch. In the case of a three-phase short-circuit fault occurring downstream of F3, the amplitude of the positive-sequence short-circuit current flowing through F3 is the smallest when the three-phase short-circuit fault occurs at the end of section Line 4. Ignoring the load impedance in the system, we can... Figure 1 Each distributed power source in the system is equivalent to a current source. ,get Figure 4 The system's positive sequence equivalent circuit is shown.

[0092] against Figure 4 The positive-sequence equivalent circuit of the system shown can be used to calculate the magnitude of the positive-sequence short-circuit current flowing through F3:

[0093] in, This indicates the current amplitude flowing through F3 when a three-phase short-circuit fault occurs downstream of the sectionalizing switch F3.

[0094] make This represents the minimum positive-sequence fault current amplitude (i.e., the reference positive-sequence short-circuit current amplitude) flowing through F3 when a three-phase short-circuit fault occurs downstream of F3, without distributed power supply access.

[0095] According to the principle of vector triangle inequality, we can obtain: In the formula, This represents the upstream line impedance coefficient, i.e., the equivalent positive-sequence impedance of the upstream line. The ratio, This represents the downstream line impedance coefficient, i.e., the equivalent positive-sequence impedance of the downstream line. The ratio.

[0096] here, ; Therefore, the minimum positive sequence short-circuit current amplitude flowing through F3 during a downstream three-phase short-circuit fault is considered to be...

[0097] The limiting circuit in a distributed power source will suppress the output current amplitude to below 1.2 times the rated current. Therefore, the minimum positive sequence short-circuit current amplitude can be approximated based on the rated parameters of each distributed power source, resulting in:

[0098] When a three-phase short-circuit fault occurs downstream of other sectionalizing switches, the calculation method for the corresponding minimum positive sequence short-circuit current amplitude is similar. It is only necessary to distinguish the relative upstream and downstream positions of the distributed power source and the sectionalizing switch, which will not be elaborated here.

[0099] Therefore, the formula for calculating the minimum positive-sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch is as follows:

[0100] By introducing upstream / downstream line impedance coefficients, this invention quantifies the proportion of the fault current output by the distributed power source that actually affects the sectionalizing switch current. Based on this, and combined with the maximum positive-sequence fault current amplitude of the distributed power source, the shunting impact of the upstream / downstream distributed power sources on the sectionalizing switch can be calculated separately, and the upstream and downstream shunting positive-sequence current amplitudes can be determined.

[0101] The present invention subtracts the positive sequence current amplitudes of each upstream shunt and each downstream shunt from the reference positive sequence short-circuit current amplitude to obtain the minimum positive sequence short-circuit current amplitude. In essence, the influence of all DGs is minimized to the greatest extent possible to reduce the current flowing through the sectionalizing switch, thereby ensuring that the minimum positive sequence short-circuit current amplitude is sufficiently safe and reliable.

[0102] This invention addresses the extremely complex interaction of fault currents caused by multi-source coupling in active distribution networks by introducing parameters such as line impedance coefficients. This decouples and quantifies the interaction into calculable influence components, thereby enabling reliable prediction of the minimum boundary of fault currents under the most unfavorable conditions.

[0103] This invention fully considers the low-voltage ride-through strategy of distributed generation (DG), deeply analyzes the maximum positive-sequence short-circuit current amplitude flowing through a sectionalizing switch during an upstream fault, and establishes a calculation method for the maximum positive-sequence short-circuit current amplitude adapted to the capacity of the DG downstream of the sectionalizing switch. Based on this, a fault direction criterion setting value calculation scheme based on the positive-sequence current amplitude is proposed. This method is simple and efficient in calculation, and can reliably ensure that the direction criterion in active distribution networks accurately distinguishes between upstream and downstream faults.

[0104] Furthermore, to address the complex scenario of distributed power sources with multiple decentralized access points, the minimum positive-sequence short-circuit current amplitude flowing during downstream faults was analyzed in depth. Based on this, a verification method for short-circuit fault setting values ​​was proposed, and the applicability judgment criteria for the positive-sequence current amplitude direction criterion were given based on the verification results.

[0105] The following simulation example illustrates the effectiveness of the three-phase short-circuit fault direction identification method provided in the embodiments of the present invention.

[0106] Build such a simulation platform Figure 1 The active power distribution network shown has the following system equivalent power supply voltage. 10.5kV, equivalent positive sequence impedance The impedance is j0.3Ω. The main transformer has a turns ratio of 110kV / 10.5kV, a rated capacity of 100MVA, and a short-circuit impedance percentage of 5%. The distribution transformers all have turns ratios of 10kV / 0.4kV, a rated capacity of 10MVA, and a short-circuit impedance percentage of 4%. The unit positive sequence impedance of the distribution line is (0.270+j0.341)Ω / km. DG1~DG4 are all photovoltaic distributed power sources, with rated three-phase active power outputs of respectively... =4 MW, =2 MW, =2 MW, =3 MW. The equivalent impedances of loads LD1, LD2, LD3, and LD4 are: = =30+j17.32Ω, = =30+j10.92Ω. The location of the fault point during the simulation is as follows: Figure 5 As shown.

[0107] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the simulation model.

[0108] S1. Data Collection: Obtain grid topology and source-load data for the active distribution network, including system-side power source equivalent voltage, system-side positive-sequence internal impedance, line equivalent impedance, and distributed generation parameters; specific parameters are shown in Table 1. Table 1

[0109] S2. Criterion for identifying the direction of three-phase short-circuit faults in active distribution networks based on positive sequence current amplitude; (1) Calculate the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch.

[0110] When a three-phase short-circuit fault occurs upstream of each section switch, the maximum positive-sequence short-circuit current amplitude flowing through each section switch is:

[0111] (2) Calculate the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch.

[0112] First, calculate the upstream line impedance coefficient for each distributed power source:

[0113] The downstream line impedance coefficients for each distributed power source are calculated as follows:

[0114] When a three-phase short-circuit fault occurs downstream of each section switch, the minimum positive-sequence short-circuit current amplitude flowing through each section switch is:

[0115] (3) Establish a criterion for identifying the direction of three-phase short-circuit faults in active distribution networks based on the positive sequence current amplitude.

[0116] The criterion for determining the direction of the three-phase short-circuit fault corresponding to each sectionalizing switch can be expressed as:

[0117] S3. Setting and verification of the criterion for identifying the direction of three-phase short-circuit faults in active distribution networks based on the positive sequence current amplitude.

[0118] (1) Calculate the setting value of the three-phase short-circuit fault direction identification criterion of the active distribution network, i.e., the short-circuit setting threshold.

[0119] Taking 1.2, the short-circuit setting thresholds corresponding to each section switch are:

[0120] The identification criteria for the direction of single-phase short-circuit faults corresponding to each section switch are as follows:

[0121] (2) Verify the short-circuit setting threshold for identifying the direction of three-phase short-circuit faults in active distribution networks.

[0122]

[0123] The verification was successful. Three-phase short-circuit faults were simulated at different fault points in the simulation platform, and the direction of the three-phase short-circuit fault was identified based on the above criteria. The positive sequence current amplitude flowing through each section switch at different fault points and the identified direction of the three-phase short-circuit fault were obtained, as detailed in Table 2. Table 2 shows that the fault direction identification results were all correct.

[0124] Table 2

[0125] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0126] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0127] Figure 6A schematic diagram of the structure of a three-phase short-circuit fault direction identification device for an active distribution network provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 6 As shown, the three-phase short-circuit fault direction identification device 6 of the active distribution network includes: an acquisition module 61, a calculation module 62 and an identification module 63.

[0128] The acquisition module 61 is used to acquire the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters. The calculation module 62 is used to calculate, based on the grid topology and the maximum positive sequence fault current amplitude, the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch for each sectionalizing switch equipped with a feeder terminal in the active distribution network. The identification module 63 is used to determine the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude.

[0129] In one possible implementation, the computation module 62 is specifically used for: For each sectionalizing switch equipped with a feeder terminal in an active distribution network, based on the grid topology, determine each distributed power source located downstream of the sectionalizing switch; The maximum positive sequence fault current amplitude of each distributed power source located downstream of the sectionalizing switch is accumulated, and the accumulated result is determined as the maximum positive sequence short-circuit current amplitude.

[0130] In one possible implementation, the computation module 62 is specifically used for: For each sectionalizing switch equipped with a feeder terminal in an active distribution network, based on the grid topology, each distributed power source upstream of the sectionalizing switch and each distributed power source downstream of the sectionalizing switch are determined respectively. For each distributed power source located upstream of the sectionalizing switch, determine the upstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the upstream line impedance coefficient, determine the upstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. For each distributed power source located downstream of the sectionalizing switch, determine the downstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the downstream line impedance coefficient, determine the downstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. Determine the reference positive sequence short-circuit current amplitude in the active distribution network; the reference positive sequence short-circuit current is used to reflect the minimum positive sequence short-circuit current amplitude when there is no distributed generation in the active distribution network; Calculate the difference between the baseline positive sequence short-circuit current amplitude and the positive sequence current amplitudes of each upstream shunt and each downstream shunt, and determine the difference as the minimum positive sequence short-circuit current amplitude.

[0131] In one possible implementation, the computation module 62 is specifically used for: Obtain the system-side power supply equivalent voltage, system-side equivalent positive sequence internal impedance, equivalent impedance of each line, and equivalent positive sequence impedance under the minimum operating mode of the system in the active distribution network; Calculate the sum of the equivalent positive sequence internal impedance of the system, the equivalent impedance of each line, and the equivalent positive sequence impedance under the minimum operating mode of the system, and determine the sum as the total equivalent positive sequence impedance of the line. The current amplitude is calculated based on the equivalent voltage of the power supply on the system side and the equivalent positive sequence total impedance of the line, and the current amplitude is determined as the reference positive sequence short-circuit current amplitude.

[0132] In one possible implementation, the identification module 63 is specifically used for: For each sectionalizing switch equipped with a feeder terminal, the short-circuit setting threshold corresponding to the sectionalizing switch is determined based on the maximum positive sequence short-circuit current amplitude. The short-circuit setting threshold is verified based on the minimum positive sequence short-circuit circuit amplitude. If the verification result of the short-circuit setting threshold is qualified, the positive sequence current amplitude of the section switch is obtained, and the direction of the three-phase short-circuit fault corresponding to the section switch is determined based on the positive sequence current amplitude and the short-circuit setting threshold.

[0133] In one possible implementation, the identification module 63 is specifically used for: For each sectionalizing switch equipped with a feeder terminal, if the positive sequence current amplitude is greater than or equal to the short-circuit setting threshold, then the three-phase short-circuit fault is determined to be located downstream of that sectionalizing switch. If the positive sequence current amplitude is less than the short-circuit setting threshold, then the three-phase short-circuit fault is determined to be located upstream of the sectionalizing switch.

[0134] In one possible implementation, the identification module 63 is specifically used for: Calculate the ratio of the minimum positive sequence short-circuit current amplitude to the short-circuit setting threshold. If the ratio is greater than the preset sensitivity coefficient, the verification result of the short-circuit setting threshold is deemed qualified.

[0135] In one possible implementation, the identification module 63 is specifically used for: For each sectionalizing switch equipped with a feeder terminal, the product of the maximum positive sequence short-circuit current amplitude and the preset reliability coefficient is determined as the short-circuit setting threshold corresponding to that sectionalizing switch.

[0136] This device embodiment can be used to implement the above method embodiment, and its technical principle and implementation effect are the same as those of the above method embodiment, so they will not be repeated here.

[0137] Figure 7 This is a schematic diagram of an electronic device provided in an embodiment of the present invention. For example... Figure 7 As shown, the electronic device 7 of this embodiment includes a processor 70 and a memory 71. The memory 71 stores a computer program 72. When the processor 70 executes the computer program 72, it implements the steps in the various method embodiments described above. Alternatively, when the processor 70 executes the computer program 72, it implements the functions of each module / unit in the various device embodiments described above.

[0138] For example, computer program 72 may be divided into one or more modules / units, which are stored in memory 71 and executed by processor 70 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 72 in electronic device 7.

[0139] Electronic device 7 may include, but is not limited to, processor 70 and memory 71. Those skilled in the art will understand that... Figure 7 This is merely an example of electronic device 7 and does not constitute a limitation on electronic device 7. It may include more or fewer components than shown, or combine certain components, or different components. For example, electronic device 7 may also include input / output devices, network access devices, buses, etc.

[0140] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0141] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0142] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for identifying the direction of a three-phase short-circuit fault in an active distribution network, characterized in that, include: Obtain the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters. For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, calculate the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch, and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch. Based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude, the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network is determined respectively.

2. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 1, characterized in that, For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch is calculated, including: For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology, each distributed power source located downstream of the sectionalizing switch is determined. The maximum positive sequence fault current amplitude of each distributed power source located downstream of the sectionalizing switch is accumulated, and the accumulated result is determined as the maximum positive sequence short-circuit current amplitude.

3. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 1, characterized in that, For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology and the maximum positive sequence fault current amplitude, calculate the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch, including: For each sectionalizing switch equipped with a feeder terminal in the active distribution network, based on the network topology, each distributed power source upstream of the sectionalizing switch and each distributed power source downstream of the sectionalizing switch are determined respectively. For each distributed power source located upstream of the sectionalizing switch, determine the upstream line impedance coefficient corresponding to each distributed power source, and based on the maximum positive sequence fault current amplitude of each distributed power source and the upstream line impedance coefficient, determine the upstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch. For each distributed power source located downstream of the sectionalizing switch, the downstream line impedance coefficient corresponding to each distributed power source is determined, and based on the maximum positive sequence fault current amplitude of each distributed power source and the downstream line impedance coefficient, the downstream shunt positive sequence current amplitude of each distributed power source for the sectionalizing switch is determined. Determine the reference positive sequence short-circuit current amplitude in the active distribution network; the reference positive sequence short-circuit current is used to reflect the minimum positive sequence short-circuit current amplitude when there is no distributed power source connected to the active distribution network; Calculate the difference between the reference positive sequence short-circuit current amplitude and the positive sequence current amplitudes of each upstream shunt and each downstream shunt, and determine the difference as the minimum positive sequence short-circuit current amplitude.

4. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 3, characterized in that, Determining the reference positive sequence short-circuit current amplitude in the active distribution network includes: Obtain the system-side power supply equivalent voltage, system-side equivalent positive sequence internal impedance, equivalent impedance of each line, and equivalent positive sequence impedance under the minimum operating mode of the system in the active distribution network. Calculate the sum of the equivalent positive sequence internal impedance of the system side, the equivalent impedance of each line, and the equivalent positive sequence impedance under the minimum operating mode of the system, and determine the sum as the total equivalent positive sequence impedance of the line; The current amplitude is calculated based on the equivalent voltage of the system-side power supply and the equivalent positive-sequence total impedance of the line, and the current amplitude is determined as the reference positive-sequence short-circuit current amplitude.

5. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to any one of claims 1-4, characterized in that, The determination of the three-phase short-circuit fault direction corresponding to each sectionalizing switch in the active distribution network based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude includes: For each sectionalizing switch equipped with a feeder terminal, the short-circuit setting threshold corresponding to the sectionalizing switch is determined based on the maximum positive sequence short-circuit current amplitude. The short-circuit setting threshold is verified based on the minimum positive sequence short-circuit circuit amplitude. If the verification result of the short-circuit setting threshold is qualified, the positive sequence current amplitude of the sectionalizing switch is obtained, and the direction of the three-phase short-circuit fault corresponding to the sectionalizing switch is determined based on the positive sequence current amplitude and the short-circuit setting threshold.

6. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 5, characterized in that, For each sectionalizing switch equipped with a feeder terminal, based on the positive sequence current amplitude and the short-circuit setting threshold, the direction of the three-phase short-circuit fault corresponding to that sectionalizing switch is determined, including: For each sectionalizing switch equipped with a feeder terminal, if the positive sequence current amplitude is greater than or equal to the short-circuit setting threshold, then it is determined that the three-phase short-circuit fault is located downstream of the sectionalizing switch. If the positive sequence current amplitude is less than the short-circuit setting threshold, then the three-phase short-circuit fault is determined to be located upstream of the sectionalizing switch.

7. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 5, characterized in that, The step of verifying the short-circuit setting threshold based on the minimum positive sequence short-circuit circuit amplitude includes: Calculate the ratio of the minimum positive sequence short-circuit current amplitude to the short-circuit setting threshold. If the ratio is greater than a preset sensitivity coefficient, then the verification result of the short-circuit setting threshold is determined to be qualified.

8. The method for identifying the direction of a three-phase short-circuit fault in an active distribution network according to claim 5, characterized in that, For each sectionalizing switch equipped with a feeder terminal, the short-circuit setting threshold corresponding to that sectionalizing switch is determined based on the maximum positive sequence short-circuit current amplitude, including: For each sectionalizing switch equipped with a feeder terminal, the product of the maximum positive sequence short-circuit current amplitude and the preset reliability coefficient is determined as the short-circuit setting threshold corresponding to that sectionalizing switch.

9. A three-phase short-circuit fault direction identification device for an active power distribution network, characterized in that, include: The acquisition module is used to acquire the grid topology and distributed generation parameters of the active distribution network, and calculate the maximum positive sequence fault current amplitude of each distributed generation in the active distribution network based on the distributed generation parameters. The calculation module is used to calculate, based on the power grid topology and the maximum positive sequence fault current amplitude, the maximum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs upstream of the sectionalizing switch and the minimum positive sequence short-circuit current amplitude flowing through the sectionalizing switch when a three-phase short-circuit fault occurs downstream of the sectionalizing switch for each sectionalizing switch equipped with a feeder terminal in the active distribution network. The identification module is used to determine the direction of the three-phase short-circuit fault corresponding to each section switch in the active distribution network based on the maximum positive sequence short-circuit current amplitude and the minimum positive sequence short-circuit current amplitude.

10. An electronic device, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 8.

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