A T-zone differential protection method, device, equipment and medium

Abstract

The application is suitable for the technical field of power system relay protection, and provides a T-zone differential protection method, device, equipment and medium. The method comprises the following steps: obtaining a differential permission mark of a current transformer configured in each branch in a T-zone, and a current differential operation mode of a differential protection device in the T-zone. According to the differential permission mark of each current transformer and the current differential operation mode of the differential protection device, a total differential permission mark of the T-zone is determined. According to the current differential operation mode of the differential protection device, a differential current and a braking current of the T-zone are determined. Based on the total differential permission mark, the differential current and the braking current, it is determined whether to control the differential protection device to perform a protection action. The abnormal working condition that all three-phase currents of a single-branch current transformer disappear can be identified, and the protection can be reliably blocked in the working condition to prevent the differential protection from malfunctioning due to a false differential current caused by a large load current.

Description

Technical Field

[0001] This application belongs to the field of power system relay protection technology, and particularly relates to a T-zone differential protection method, device, equipment and medium. Background Technology

[0002] In power systems, under connection types such as 3 / 2 and 3 / 4, if the outgoing line connected by double circuit breakers (i.e., the side circuit breaker and the interrupt circuit breaker) is also equipped with a separate current transformer, and the protection of the outgoing line uses the current transformer of the outgoing line, the protection range of the outgoing line does not include the T-shaped area between the double circuit breaker and the current transformer of the outgoing line. Therefore, a differential protection device needs to be configured for this part.

[0003] Zone T protection typically employs a differential principle. If, during normal operation, a single-phase or two-phase current disappears from any current transformer (CT), existing technology can identify this using CT disconnection detection methods, preventing malfunction of the zone T differential protection device. However, when all three-phase currents of a current transformer on a branch disappear, existing technology cannot detect this. If the load current is large at this time, a significant differential current will be generated, leading to malfunction of the zone T differential protection device. Therefore, providing a method to prevent malfunction of the zone T differential protection device when all three-phase currents of current transformers on one branch disappear has become a pressing issue. Summary of the Invention

[0004] This application provides a T-zone differential protection method, device, equipment, and medium, which can solve the problem that existing T-zone differential protection methods can identify single-phase or two-phase current loss faults in single-branch current transformers, but cannot identify the condition where all three-phase currents of a single-branch current transformer are lost, and generate false differential currents when the load current is large, causing the differential protection device to malfunction.

[0005] In a first aspect, embodiments of this application provide a T-zone differential protection method, including: Obtain the differential allow flag of the current transformer configured in each branch in zone T, and the current differential operation mode of the differential protection device in zone T, wherein zone T is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node; The total differential allowance flag of zone T is determined based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device; Based on the current differential operation mode of the differential protection device, determine the differential current and braking current in zone T; Based on the total differential allowance flag, the differential current, and the braking current, determine whether to control the differential protection device to perform a protection action.

[0006] In one possible implementation of the first aspect, obtaining the differential allowance flag of the current transformer configured for each branch in region T includes: The current frequency change of the current transformer configured for each branch is calculated phase by phase. If the frequency change corresponding to a preset number of consecutive sampling points is greater than a preset change threshold, the current transformer is determined to meet the change start condition. The three-phase current amplitude of the current transformer configured in each branch is monitored in real time. If the three-phase no-current state of the current transformer continues for a preset time, it is determined that the current transformer is in a state of no current in all three phases. When the current transformer meets the change start condition, or is in a state where all three phases are without current, the differential allowable flag of the current transformer is determined to be an allowable flag. When the current transformer does not meet the change-of-current start-up conditions and is not in a state where all three phases are without current, the differential allow flag of the current transformer is determined to be a prohibition flag.

[0007] In one possible implementation of the first aspect, the plurality of branches include a first branch configured with a first current transformer, a second branch configured with a second current transformer, and a third branch configured with a third current transformer; obtaining the current differential operation mode of the differential protection device in the T zone includes: When the switch of the third branch is in the closed state, the current differential operation mode of the differential protection device is determined to be the three-sided differential operation mode; When the switch of the third branch is in the open state, the current differential operation mode of the differential protection device is determined to be the two-sided differential operation mode.

[0008] In one possible implementation of the first aspect, determining the total differential allowance flag of the T zone based on the differential allowance flag of each of the current transformers and the current differential operation mode of the differential protection device includes: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, if both the differential allowance flag of the first current transformer and the differential allowance flag of the second current transformer are the allowance flags, then the total differential allowance flag of zone T is determined to be the allowance flag; and, If the differential allow flag of the first current transformer or the differential allow flag of the second current transformer is the prohibition flag, then the total differential allow flag of the T zone is determined to be the prohibition flag; When the current differential operation mode of the differential protection device is the three-sided differential operation mode, if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0, and there are at least two current transformers whose differential allowance flag is the allowance flag, then the total differential allowance flag of the T zone is determined to be the allowance flag; and, If the number of current transformers in the first, second, and third current transformers that are all in a three-phase no-current state is 1, and the differential allowance flags of the remaining two current transformers are both the allowance flag, then the total differential allowance flag of the T-zone is determined to be the allowance flag; and, If the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0 and the number of current transformers with the permission flag is less than two, or if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 1 and the differential permission flag of at least one of the remaining two current transformers is the prohibition flag, then the total differential permission flag of the T-zone is determined to be the prohibition flag.

[0009] In one possible implementation of the first aspect, determining the differential current and braking current in zone T based on the current differential operation mode of the differential protection device includes: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, the vector sum of the current of the first branch and the current of the second branch is taken as the differential current of the T zone; and the sum of the magnitudes of the current of the first branch and the current of the second branch is taken as the braking current of the T zone. When the current differential operation mode of the differential protection device is the three-sided differential operation mode, the vector sum of the current of the first branch, the current of the second branch, and the current of the third branch is taken as the differential current of the T zone; and the sum of the amplitudes of the current of the first branch, the current of the second branch, and the current of the third branch is taken as the braking current of the T zone.

[0010] In one possible implementation of the first aspect, determining whether to control the differential protection device to perform a protection action based on the total differential allowance flag, the differential current, and the braking current includes: When the differential current is greater than a preset differential current threshold, the ratio of the differential current to the braking current is greater than a preset proportional coefficient, and the total differential allowance flag is the allowance flag, the differential protection device is controlled to perform a protection action. When the differential current is greater than the preset differential current threshold, the ratio of the differential current to the braking current is greater than the preset proportional coefficient, but the total differential allow flag is the prohibition flag, the differential protection device is not controlled to perform protection action.

[0011] Secondly, embodiments of this application provide a T-zone differential protection device, comprising: The acquisition module is used to acquire the differential allow flag of the current transformer configured in each branch in the T zone, as well as the current differential operation mode of the differential protection device in the T zone, wherein the T zone is a T-shaped topology electrical area formed by the convergence of the multiple branches at the same electrical node; The determination module is used to determine the total differential permission flag of the T zone based on the differential permission flag of each current transformer and the current differential operation mode of the differential protection device; The calculation module is used to determine the differential current and braking current in zone T based on the current differential operation mode of the differential protection device. The judgment module is used to determine whether to control the differential protection device to perform a protection action based on the total differential allowance flag, the differential current, and the braking current.

[0012] Thirdly, embodiments of this application provide a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the T-zone differential protection method described in any of the above claims.

[0013] Fourthly, embodiments of this application provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the T-zone differential protection method described in any of the preceding claims.

[0014] Fifthly, embodiments of this application provide a computer program product that, when run on a terminal device, causes the terminal device to execute the T-zone differential protection method described in any one of the first aspects.

[0015] The beneficial effects of the embodiments in this application compared with the prior art are: This application provides a T-zone differential protection method, comprising: First, obtaining the differential allowance flag of the current transformer configured in each branch of the T-zone, and the current differential operation mode of the differential protection device in the T-zone, wherein the T-zone is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node. Then, determining the total differential allowance flag of the T-zone based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device. Determining the differential current and restraining current of the T-zone based on the current differential operation mode of the differential protection device. Finally, determining whether to control the differential protection device to perform a protection action based on the total differential allowance flag, the differential current, and the restraining current. This method identifies the differential allowance flag of the current transformer branch by branch-by-branch and generates a total differential allowance flag in combination with the current differential operation mode. This enables effective identification of the condition where all three-phase currents of a single branch current transformer disappear. When a false differential current is generated under a large load current in this condition, the protection output is reliably blocked to avoid maloperation of the differential protection. At the same time, the differential protection can be opened normally to achieve fault tripping when there is a fault in the actual zone, thus taking into account both the reliability of protection operation and the sensitivity of fault action. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a typical T-zone differential protection wiring diagram in the existing technology; Figure 2 This is a schematic flowchart of a T-zone differential protection method provided in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of a T-zone differential protection device provided in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a terminal device provided in an embodiment of this application. Detailed Implementation

[0018] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0019] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0020] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if detected [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once detected [the described condition or event]," or "in response to detection [the described condition or event]."

[0022] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0024] First, some terms used in the embodiments of this application will be explained to facilitate understanding by those skilled in the art.

[0025] A T-zone refers to a T-shaped electrical topology region formed by multiple branches converging at the same electrical node, such as... Figure 1 As shown in the image.

[0026] Current transformers (CTs) are current sampling elements connected in series in each branch to collect the primary current of the branch and convert it into secondary current, which is then sent to the differential protection device. Each branch in the online T zone is equipped with an independent current sensor.

[0027] The differential allowance flag indicates that a current transformer on a corresponding single branch is eligible to participate in differential calculations. The differential allowance flag is either "1" (allowed) or "0" (prohibited). When the differential allowance flag of a current transformer is "allowed," it means that the current of that current transformer can participate in differential calculations; when the differential allowance flag of a current transformer is "prohibited," it means that the current of that current transformer will not participate in differential calculations and must be excluded.

[0028] The differential protection device is a protection device deployed in zone T that can realize differential protection in zone T. This differential protection device can collect the current of the current transformers of all branches to complete the differential criterion calculation, fault identification, and trip output.

[0029] The above is a brief introduction to the terms used in the embodiments of this application, and will not be repeated below.

[0030] like Figure 1 As shown, Figure 1 This is a typical wiring diagram of T-zone differential protection in existing technology. Figure 1 In this circuit, CB1, CB2, CB4, and CB5 are circuit breakers. Three current transformers (CTs) are connected to the T zone, including the first current transformer CT1 (located in the branch where the side circuit breaker CB1 is located), the second current transformer CT2 (located in the branch where the interrupt circuit breaker CB2 is located), and the third current transformer CT3 (located in the outgoing line), forming a three-sided differential circuit. If there is also a disconnector on the outgoing line, the circuit breakers in this string need to continue operating when the disconnector is open. In this case, the T zone uses the first current transformer CT1 and the second current transformer CT2 to form a two-sided differential circuit.

[0031] Zone T protection typically employs a differential principle. If, during normal operation, a single-phase or two-phase current disappears from any current transformer (CT), existing technology can identify this using CT disconnection detection methods, preventing malfunction of the zone T differential protection device. However, when all three-phase currents of a current transformer on a branch disappear, existing technology cannot detect this. If the load current is large at this time, a significant differential current will be generated, leading to malfunction of the zone T differential protection device. Therefore, providing a method to prevent malfunction of the zone T differential protection device when all three-phase currents of the current sensors on one branch disappear has become a pressing issue.

[0032] Please see Figure 2 , Figure 2 This is a flowchart illustrating a T-zone differential protection method according to an embodiment of this application. As an example and not a limitation, this method can be operated on or applied to a terminal device, and the method includes: S11. Obtain the differential allow flag of the current transformer configured in each branch in zone T, and the current differential operation mode of the differential protection device in zone T. Zone T is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node.

[0033] S12. Determine the total differential allowance flag for zone T based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device.

[0034] S13. Determine the differential current and braking current in zone T based on the current differential operation mode of the differential protection device.

[0035] S14. Based on the total differential allowance flag, differential current, and braking current, determine whether to control the differential protection device to perform protection actions.

[0036] The differential operation mode refers to the predefined working mode of the differential protection device. This differential operation mode can be switched automatically or manually according to the operating wiring and branch activation / deactivation status of the T zone. This differential operation mode is used to characterize the number of effective branches in the current T zone and can guide the dynamic switching of calculation formulas such as differential current and braking current.

[0037] The overall differential protection permission flag refers to the overall criterion for allowing differential protection to be activated in area T. This flag is determined jointly by the differential protection permission flags of all branch current transformers and the current differential operation mode, indicating whether the entire area T meets the preconditions for differential protection activation. In some examples, this flag can be "1" (permission flag) or "0" (prohibition flag).

[0038] For an electrical node (i.e., the bus node in area T in this embodiment), according to Kirchhoff's current law: under steady state, the differential current is calculated by summing the vector currents flowing into the node equal to summing the vector currents flowing out of the node. That is, the differential current is obtained by vector summing the currents of all branches. ;in, For differential current, This represents the current phasor (including magnitude and phase) for each branch involved in the calculation. This differential current can be used to determine whether a short-circuit fault has occurred within region T.

[0039] The braking current is a characteristic quantity used by differential protection to prevent maloperation caused by saturation of the current transformer during faults outside the protection zone. Generally, this braking current is calculated by combining the current amplitudes of each branch (e.g., maximum value, average value, summation, etc.).

[0040] Specifically, the T-zone adaptive differential protection method provided in this embodiment can be divided into four core steps. First, it iterates through the current transformers corresponding to each branch in the T-zone, obtains the differential allowance flag for each transformer, and reads the current differential operation mode of the differential protection device to determine which branches in the T-zone are currently energized. In some examples, the differential allowance flag of the current transformer can be determined branch by branch using the current frequency change criterion and the three-phase no-current state criterion. The differential operation mode can be adaptively determined by the switch opening / closing position of the third branch, divided into two-sided and three-sided topology modes. This step achieves a comprehensive perception of the primary operating topology and the real-time operating conditions of each branch, providing basic parameters for subsequent adaptive calculations.

[0041] Secondly, after obtaining the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device, based on whether the current operation mode is two-sided or three-sided, differentiated logic is used to summarize the differential allowance status of all branches and determine the total differential allowance flag of zone T. This enables adaptive verification of differential protection activation / deactivation conditions, allowing reliable blocking of differential protection during branch maintenance or current transformer anomalies, thus avoiding risks caused by erroneous calculations. In some examples, the two-sided differential operation mode requires both operating branches to have allowance flags before differential protection can be activated; the three-sided differential operation mode is compatible with both full-branch energized and single-branch unloaded normal operating conditions, requiring effective disturbance conditions of multiple branches to be met before differential protection can be activated. This step achieves a hierarchical enabling mechanism that enables precise blocking of single branches and overall controllability across the entire region.

[0042] Then, the set of current branches that can effectively participate in the calculation is selected by the differential operation mode, and branches that are out of service or under maintenance are automatically removed. The differential current is obtained by vector calculation using the current of the selected effective branches, and the braking current is obtained by amplitude calculation using the current of the selected effective branches. By adapting to the flexible operation mode of zone T, the matching of the differential current and braking current calculation models with the actual topology is ensured under different operating configurations.

[0043] Finally, by combining the total differential allowance flag, differential current, and braking current, it is determined whether to control the differential protection device to trigger protection action. A dual verification method using electrical ratio criteria and operating condition blocking criteria is employed. In some examples, when the electrical quantities meet the differential current over-limit and ratio over-limit requirements, and the total differential allowance flag is enabled, it is determined to be a real fault, and the differential protection device is controlled to perform protection action. When the electrical quantities meet the differential current over-limit and ratio over-limit requirements, but the total differential allowance flag is disabled, it is determined to be a steady-state false differential current, and the protection output is reliably blocked without tripping.

[0044] It should be understood that this embodiment identifies the differential allowance flag of the current transformer branch by distinguishing the differential allowance flag of the current transformer branch by branch and generates the total differential allowance flag by combining the current differential operation mode. This enables effective identification of the condition where all three-phase currents of a single branch current transformer disappear. When a false differential current is generated under a large load current in this condition, the protection output is reliably blocked to avoid maloperation of the differential protection. At the same time, the differential protection can be opened normally to achieve fault tripping when there is a fault in the real zone, thus taking into account both the reliability of protection operation and the sensitivity of fault action.

[0045] In some examples, multiple branches include a first branch configuring a first current transformer, a second branch configuring a second current transformer, and a third branch configuring a third current transformer.

[0046] like Figure 1 In zone T, the circuit may include a first branch equipped with a first current transformer CT1, a second branch equipped with a second current transformer CT2, and a third branch (i.e., a lead-out line) equipped with a third current transformer CT3. The differential protection can be connected to these three current sources to form a multi-sided differential protection system. Figure 1 The knife switch in the middle is the switch in the third branch.

[0047] One possible implementation involves obtaining the differential allowance flag of the current transformer configured in each branch of area T in step S11, including: The current frequency change of the current transformer configured for each branch is calculated phase by phase. If the frequency change corresponding to a preset number of consecutive sampling points is greater than a preset change threshold, it is determined that the current transformer meets the change start condition.

[0048] The three-phase current amplitude of the current transformer configured in each branch is monitored in real time. If the three-phase current-free state of the current transformer continues for a preset time, it is determined that the current transformer is in a state of no current in all three phases.

[0049] When the current transformer meets the change-of-current start-up conditions, or is in a state where all three phases are without current, the differential allowable flag of the current transformer is determined as the allowable flag.

[0050] When the current transformer does not meet the change-of-current start-up conditions and is not in a state where all three phases are without current, the differential operation permission flag of the current transformer is determined to be a prohibition flag.

[0051] The current cycle variation refers to the change in current amplitude / phasor between adjacent cycles, calculated independently for each of the three phases (A, B, and C) at the power frequency (e.g., 50Hz / 20ms per cycle). A sampling point can be understood as a discrete data point of the secondary current of the current transformer collected by the analog-to-digital converter (AD) of the protection device at a fixed frequency; multiple sampling points constitute one power frequency cycle. The continuously preset number of sampling points can be understood as a criterion for jitter prevention; it requires that the exceeding limit condition be met for several consecutive sampling cycles to avoid misjudgments caused by instantaneous pulse noise and electromagnetic interference. In this embodiment, the specific value of the preset number is not limited; the preset number is a configurable parameter.

[0052] The preset change threshold is a pre-defined threshold value for the change in current frequency. If the change in current frequency exceeds this preset threshold, a significant sudden change in current can be determined. This preset change threshold can be set according to factors such as line load level and grid noise level; this embodiment does not limit the specific value of the preset change threshold. The change trigger condition is a criterion for fault characteristics. When the current experiences a sudden increase or decrease (short-circuit fault, line switching, large load switching, etc.), and the frequency change continuously exceeds the limit, it can be determined that there is a transient current disturbance, and a fault condition is highly probable.

[0053] Three-phase current amplitude refers to the effective value amplitude of the A, B, and C phase currents extracted from the current transformer, determining only the current magnitude. A state with no current in all three phases can be understood as the current amplitudes of phases A, B, and C all being below the minimum current threshold (close to zero current), indicating that the branch is in a no-load, out-of-operation, or switch-off state. A preset time is used as the criterion for confirming no current, preventing instantaneous leakage current, zero-point drift, and sampling noise from misjudging no current. Only when the no-current condition is continuously met for the preset time can the branch be confirmed as truly no-load.

[0054] Specifically, in this embodiment, the differential allowance flag of the current transformer configured in each branch of area T is obtained, and the specific implementation process is as follows: The following discrimination logic is executed independently for the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3.

[0055] First, the current frequency change flowing through each current transformer is calculated phase by phase. The protection device performs calculations for the A, B, and C phases corresponding to the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3, respectively. Current characteristic quantities are extracted using the power frequency as the base window, and the difference between current characteristic quantities between adjacent cycles is calculated to obtain the current frequency change. The sampling data is continuously monitored. If the frequency change corresponding to a preset number of consecutive sampling points is greater than a preset change threshold, the corresponding current transformer is determined to meet the change-based activation condition. It should be understood that using phase-by-phase frequency change for discrimination can filter out high-frequency sampling noise and instantaneous electromagnetic interference in the field, effectively capturing current surges caused by short-circuit faults and large-capacity load switching. Simultaneously, relying on continuous sampling point constraints avoids false activation due to instantaneous interference, reliably identifying various asymmetrical faults such as single-phase and multi-phase faults.

[0056] In one example, the criterion for triggering the change is: , , It is the change in current within one power frequency cycle (cycle change), which is the absolute value calculated by subtracting the instantaneous current value of the sampling point one cycle ago from the instantaneous current value of the current at the current sampling point. In this embodiment, the preset change threshold for initiating the change is 0.05In, where In is the secondary rated value of the current transformer. For example, when this criterion is met for three consecutive sampling points, the current transformer is considered to meet the change initiation condition.

[0057] Secondly, the three-phase current amplitude of each current transformer is monitored in real time. The three-phase current outputs of the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3 are continuously collected and the current amplitude is calculated. It is determined in real time whether the three-phase current is simultaneously below the no-current threshold. If the three-phase no-current state of a certain current transformer continues for a preset time, it is determined that the current transformer is in a state of no current in all three phases. It should be understood that the preset time constitutes an anti-jitter confirmation mechanism to overcome the instantaneous no-current misjudgment caused by sampling zero-point drift and weak leakage current in the line, and to accurately identify the corresponding branch switch tripping and line no-load shutdown conditions.

[0058] In some examples, the criterion for a three-phase no-current state is: ; in, This refers to the amplitude of the A-phase current of the current transformer. This refers to the amplitude of the B-phase current of the current transformer. This refers to the amplitude of the C-phase current of the current transformer. For example, if this criterion is met continuously for 25 seconds, the current transformer is considered to be in a state of no current in all three phases.

[0059] Subsequently, the differential allowance flag for each current transformer is determined based on the results of two criteria. The differential allowance flag controls whether the corresponding branch current participates in the differential current calculation and is divided into an allowance flag and a prohibition flag. For any one of the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3, when it meets the change in current initiation condition or is in a state where all three phases are without current, the differential allowance flag of that current transformer is determined to be an allowance flag, that is, the differential allowance flag of that current transformer is 1. Among them, meeting the change in current initiation condition indicates that there is a fault or transient disturbance in the power grid, and differential calculation needs to be enabled to ensure rapid fault identification; the state where all three phases are without current corresponds to the branch operating under no-load, and the branch current is approximately zero. Accessing the differential calculation will not introduce false differential current, and the branch operating status can be continuously monitored.

[0060] When a current transformer neither meets the change-of-current start-up conditions nor is in a state where all three phases are without current, it indicates that the corresponding branch is in a steady-state, stable load-bearing operation. In this case, the differential allowance flag of the current transformer is set to the prohibition flag, meaning the differential allowance flag is 0. Under steady-state load-bearing conditions, due to the influence of current transformer transmission errors and secondary sampling deviations, if all branches continuously participate in differential calculations, steady-state false differential currents can easily be generated, leading to maloperation of the differential protection. By prohibiting the corresponding branch from participating in differential calculations, steady-state false differential currents can be suppressed, improving the reliability of protection operation.

[0061] It should be understood that in this embodiment, a parallel independent discrimination mechanism is adopted for the current transformers of each branch in Zone T, which can simultaneously update the differential protection flags corresponding to the first, second, and third branches. Relying on the coordinated action of the change-initiation criterion and the three-phase no-current criterion, it adaptively distinguishes three typical operating conditions: fault disturbance, branch no-load, and steady-state load. This ensures the sensitivity of differential protection operation under fault scenarios while suppressing false differential current and preventing maloperation under normal load conditions, adapting to the multi-branch topology characteristics of Zone T. Various discrimination thresholds, the number of continuous sampling points, and the duration of the state can be flexibly adjusted, implemented only through software logic without requiring hardware modifications. This facilitates upgrades and applications within existing Zone T differential protection devices, demonstrating strong engineering practicality.

[0062] One possible implementation involves obtaining the current differential operation mode of the differential protection device in zone T in step S11, including: When the switch of the third branch is in the closed state, the current differential operation mode of the differential protection device is determined to be the three-sided differential operation mode.

[0063] When the switch of the third branch is in the open state, the current differential operation mode of the differential protection device is determined to be the two-sided differential operation mode.

[0064] The switch for the third branch refers to the disconnecting switch installed on the third branch, used to control the operation and shutdown of the third branch. A closed switch indicates that the third branch is in operation, and an open switch indicates that the third branch is out of operation.

[0065] Differential operation mode refers to the internal working mode identifier of the differential protection device, which dynamically switches according to the number of branches in operation, determining the number of branches participating in the differential current calculation and the differential operation logic. In this embodiment, the differential operation mode can include three-sided differential operation mode and two-sided differential operation mode. The three-sided differential operation mode can be understood as all three branches (the first, second, and third branches) participating in differential operation, with the differential protection device collecting the three-phase currents from the first current transformer CT1, the second current transformer CT2, and the third current transformer CT3, and executing the three-sided current differential criterion. The two-sided differential operation mode can be understood as the third branch switch being open and off, with only the first and second branches participating in the differential operation, and the differential protection device using two-sided differential operation logic.

[0066] Specifically, the current differential operation mode of the T-zone differential protection device is determined using the following logic: The position signal of the third branch switch is acquired in real time to identify the actual operating status of the switch. If the switch of the third branch is detected to be in a closed state, it indicates that the third branch is normally connected to the power grid and there is a current transmission channel. At this time, the current differential operation mode of the differential protection device can be determined to be a three-sided differential operation mode. In this case, the first, second, and third branches are all included in the differential protection calculation scope, and the differential protection device performs differential current calculation and fault identification according to the three-sided differential principle.

[0067] If the switch of the third branch is detected to be in the open state, it indicates that the third branch is out of operation and there is no longer any load current or fault current flowing through it. At this time, it can be determined that the current differential operation mode of the differential protection device is the two-sided differential operation mode. In this case, only the first and second branches participate in the differential operation, and the current path of the out-of-operation third branch is excluded.

[0068] It is understood that this embodiment relies on the position of the third branch switch to achieve automatic switching of differential operation mode, ensuring that the protection calculation model remains consistent with the actual operating topology of the primary power grid. Compared to traditional differential protection with a fixed operation mode, it effectively avoids the false differential current problem caused by sampling noise of the third current transformer and imbalance of the secondary circuit under long-term outage of the third branch. At the same time, it eliminates the need for maintenance personnel to modify the protection control words and the on / off function pressure plates on-site, reducing the workload of on-site maintenance and the risk of misoperation. The differential operation mode selection logic can cooperate with the differential permission flag discrimination logic of the current transformers of each branch mentioned above: the differential operation mode completes the macroscopic calculation architecture switching under the long-term on / off scenario of the branch, and the differential permission flag realizes the millisecond-level dynamic on / off control of the branch transient and no-load conditions under the same operation mode. The two work together in a layered manner to further improve the steady-state anti-maloperation capability and fault response sensitivity of the T-zone differential protection. All discrimination logics are implemented by software, requiring only the connection of the switch position signal, without the need to modify the primary equipment, which facilitates engineering implementation.

[0069] One possible implementation is that, in step S12, the total differential allowance flag for zone T is determined based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device, including: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, if both the differential allowance flags of the first current transformer and the second current transformer are allowance flags, then the total differential allowance flag for zone T is determined to be the allowance flag. Also, If the differential allow sign of the first current transformer or the differential allow sign of the second current transformer is a prohibit sign, then the total differential allow sign of zone T is determined to be a prohibit sign.

[0070] When the current differential operation mode of the differential protection device is three-sided differential operation mode, if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0, and there are at least two current transformers whose differential allowance flags are valid, then the total differential allowance flag for zone T is determined to be valid. Furthermore, If the number of current transformers in the first, second, and third current transformers that are all in a state of no current in each of the three phases is 1, and the differential allowance flags of the remaining two current transformers are both allowance flags, then the total differential allowance flag for zone T is determined to be the allowance flag. And, If the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0 and the number of current transformers with permission flags is less than two, or if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 1 and the differential permission flag of at least one of the remaining two current transformers is a prohibition flag, then the total differential permission flag of zone T is determined to be a prohibition flag.

[0071] In this embodiment, based on two types of input conditions—the independent differential permission flag for each current transformer and the current differential operation mode of the differential protection device—the overall differential permission flag is determined in stages. The overall differential permission flag is used to control whether the differential fault discrimination logic of the entire differential protection system in Zone T is activated, and includes two states: permission flag and prohibition flag. The determination of the overall differential permission flag in Zone T can be divided into two main branches of logic.

[0072] Branch 1: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, only the first current transformer and the second current transformer participate in the logic judgment.

[0073] As shown in Table 1, Table 1 is the determination table for the total differential allowable flag under the two-sided differential operation mode. In Table 1, if both the differential allowable flags of the first current transformer CT1 and the second current transformer CT2 are allowable flags, then the total differential allowable flag for zone T is determined to be allowable flag 1. If either the differential allowable flag of the first current transformer CT1 or the differential allowable flag of the second current transformer CT2 is a prohibitive flag, then the total differential allowable flag for zone T is determined to be prohibitive flag 0. Under the two-sided differential operation mode, both branches need to simultaneously meet the differential activation conditions. When either branch is under steady-state load conditions, continuous activation of the entire differential protection system can easily generate steady-state false differential current. Therefore, the differential protection is completely blocked.

[0074] Table 1. Determination of Total Differential Allowance Flags under Two-Sided Differential Operation Mode

[0075] Branch 2: When the current differential operation mode of the differential protection device is the three-sided differential operation mode, the operating conditions of the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 are identified simultaneously.

[0076] In the first scenario, if the number of current transformers (CT1, CT2, and CT3) in a three-phase no-current state is 0, and at least two of the current transformers have a differential allowance flag of 1, then the total differential allowance flag for zone T is determined to be flag 1. That is, if all three current transformers are connected and have current, the total differential allowance flag is two out of three current transformers with differential allowance flags of 1; if two or more current transformers have differential allowance flags of 0, then the total differential allowance flag is 0. As shown in Table 2, Table 2 is the determination table for the first scenario of the total differential allowance flag under three-phase differential operation. As shown in Table 2, when CT1, CT2, and CT3 all have current, meaning they are not in a state where all three phases are without current, if the differential allowable flag of CT1 and CT2 is 1, then the total differential allowable flag is 1; if the differential allowable flags of CT1 and CT2 are both 0, then the total differential allowable flag is 0.

[0077] Table 2. Determination of the First Case of Total Differential Permissible Flag under Three-Sided Differential Operation Mode

[0078] In the second scenario, if one of the three current transformers (CT1, CT2, and CT3) is in a state of no current in all three phases, and the differential allowance flags of the remaining two current transformers are both allowance flag 1, then the total differential allowance flag for zone T is determined to be allowance flag 1. That is, if a current transformer is in a state of no current in all three phases, its differential allowance flag is not considered. In this case, the differential allowance flags of the other two current transformers are taken, and if both of these flags are allowance flag 1, the total differential allowance flag is allowance flag 1. If either of the other two current transformers has a prohibition flag 0, then the total differential allowance flag is prohibition flag 0. As shown in Table 3, Table 3 is the second scenario determination table for the total differential allowance flag under the three-sided differential operation mode. As shown in Table 3, when CT1 is in a state where all three phases are without current, if the differential allowable flag of CT2 and CT3 is allowable flag 1, then the total differential allowable flag is allowable flag 1; if any one of the differential allowable flags of CT2 and CT3 is prohibitive flag 0, then the total differential allowable flag is prohibitive flag 0.

[0079] Table 3. Determination of the Second Case of Total Differential Permissible Flag under Three-Sided Differential Operation Mode

[0080] It should be understood that this step can be adapted to common T-zone topology conditions where all three branches are energized or a single branch is out of service under no-load. When multiple branches are operating smoothly under load simultaneously, and only a single branch experiences current fluctuations, the differential protection flag is blocked, thus avoiding maloperation of the differential protection caused by sampling deviations or unidirectional load fluctuations.

[0081] It is understood that this embodiment relies on branch-level differential protection enable flags and differential operation modes to generate a total differential protection enable flag in a hierarchical manner, forming a two-level control architecture of refined branch enablement and overall protection enablement. Differential discrimination criteria are configured for two-sided and three-sided differential operation modes to adaptively match the primary topology changes caused by the switching of the third branch; simultaneously, the number of branches under no-load conditions is distinguished in the three-sided mode to accommodate diverse operating conditions of multiple branches. During normal steady-state operation of the power grid, it effectively suppresses false differential currents and reduces the risk of differential protection maloperation; when a short-circuit fault causes a sudden change in current in multiple branches, the total differential protection enable flag can be set in a timely manner to ensure reliable start-up of differential protection, balancing protection operation safety and fault response sensitivity. The entire discrimination logic is based on existing sampling data and switch position signals of the device, requiring no additional primary equipment, and the parameter configuration is flexible, facilitating its widespread application in T-zone differential protection device projects.

[0082] One possible implementation involves determining the differential current and braking current in zone T in step S13, based on the current differential operation mode of the differential protection device, including: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, the vector sum of the current in the first branch and the current in the second branch is taken as the differential current in zone T. Furthermore, the sum of the amplitudes of the current in the first branch and the current in the second branch is taken as the braking current in zone T.

[0083] When the current differential operation mode of the differential protection device is three-sided differential operation mode, the vector sum of the currents in the first branch, the second branch, and the third branch is taken as the differential current in zone T. Additionally, the sum of the magnitudes of the currents in the first branch, the second branch, and the third branch is taken as the braking current in zone T.

[0084] Vector sum refers to the simultaneous use of current amplitude and phase to perform phasor operations (planar vector addition), which is the basic operation for differential protection to achieve fault identification. Amplitude sum refers to the arithmetic addition of the effective values ​​(amplitudes) of the current in each branch, without considering the current phase, and only represents the total load flow of the current system.

[0085] The differential current in region T is calculated as follows: In three-sided differential operation mode, differential current The vector sum of the currents from the three current transformers is: In differential operation mode, the differential current... The vector sum of the currents from the two current transformers is: ;in, Let be the current phasor of the first branch. For the current phasor of the second branch, This is the current phasor of the third branch.

[0086] The braking current in zone T is calculated as follows: In three-sided differential operation mode, braking current The sum of the current amplitudes of the three current transformers is: When operating in differential mode on both sides, the braking current... The sum of the current amplitudes of the two current transformers is: ;in, The magnitude of the current phasor in the first branch. This represents the magnitude of the current phasor in the second branch. This represents the magnitude of the current phasor in the third branch.

[0087] The differential current is used to determine whether a short-circuit fault has occurred in zone T, while the braking current is used to construct the ratio braking characteristic, suppress unbalanced current caused by load imbalance, current transformer transmission error, and external faults, and prevent differential protection from malfunctioning.

[0088] When the current differential operation mode of the differential protection device is the two-sided differential operation mode, the current of the first branch and the current of the second branch are vector-summed to obtain the differential current in zone T; simultaneously, the current amplitudes of the first branch and the second branch are arithmetically added, and the sum is used as the braking current in zone T. In the two-sided differential operation mode, the third branch is electrically isolated and out of operation, and its current is no longer included in the calculation to avoid the sampling noise of the out-of-operation branch affecting the accuracy of the differential current calculation.

[0089] When the current differential operation mode of the differential protection device is three-sided differential operation mode, the currents of the first branch, the second branch, and the third branch are vector-summed to obtain the differential current in zone T; simultaneously, the amplitudes of the currents of the first, second, and third branches are arithmetically added, and the sum is used as the braking current in zone T. The three-sided differential operation mode is compatible with operating topologies where all three branches are connected, comprehensively collecting the currents of all operating branches to ensure accurate calculation of the differential current during faults within the zone.

[0090] It should be understood that this embodiment can automatically switch the calculation models for differential current and braking current according to the switching status of the third branch, ensuring that the current calculation model remains consistent with the actual topology of the primary power grid. Compared to the approach of always using a fixed three-sided current calculation formula, this embodiment automatically eliminates the current of the third branch when it is out of service, effectively eliminating the additional unbalanced differential current caused by zero-point drift of the current transformer and sampling interference in the out-of-service branch. This step, in conjunction with the aforementioned differential operation mode identification logic and total differential allowance flag discrimination logic, forms a complete adaptive control link for T-zone differential protection, improving the accuracy of fault identification and further enhancing the reliability of steady-state protection operation.

[0091] One possible implementation involves determining, in step S14, whether to control the differential protection device to perform a protection action based on the total differential enable flag, differential current, and braking current, including: When the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, and the total differential allowance flag is set to allow, the differential protection device is controlled to perform protection actions.

[0092] If the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, but the total differential allow sign is the prohibit sign, then the differential protection device will not be controlled to perform protection actions.

[0093] The preset differential current threshold refers to a fixed operating current threshold value pre-configured for the differential protection device. It is the basic absolute criterion for starting the differential protection and can be used to shield the small differential current generated by the inherent error of the current transformer, zero sampling drift, and slight load imbalance. Only when the differential current exceeds the preset differential current threshold can the basic conditions for protection operation be met.

[0094] The ratio of differential current to braking current is a relative characteristic quantity used to characterize the degree of current imbalance in the system, eliminating the influence of load size on fault identification and achieving accurate fault identification under light and heavy load conditions. The preset proportional coefficient, also known as the ratio braking coefficient, is a core setting parameter of the ratio differential protection. It characterizes the degree of abnormality of the differential current relative to the braking current, adaptively raising the operating threshold through the braking current to avoid maloperation due to unbalanced current under conditions of external faults or heavy load crossings. In this example, the preset proportional coefficient can be 0.5 in three-sided differential operation mode and 0.6 in two-sided differential operation mode.

[0095] In this embodiment, a dual discrimination mechanism combining electrical quantity criteria and operating condition permission flags is adopted. The ratio braking differential characteristics are used as the basis for fault identification, and the total differential permission flag is used as the operating condition blocking condition, which together determine the protection exit behavior.

[0096] Specifically, when the real-time calculated differential current exceeds the preset differential current threshold, and the ratio of differential current to braking current exceeds the preset proportional coefficient, while the total differential allowance flag in zone T is flag 1, it indicates that the current power grid is under effective operating conditions such as fault disturbance and branch no-load, which allow differential protection to be activated. At this time, it is determined that the current excessive differential current is an effective differential current caused by a real fault, rather than a false differential current caused by non-steady-state load imbalance and sampling error. The differential protection device is then controlled to perform a protection trip action to quickly clear the fault and achieve rapid fault isolation.

[0097] When the differential current exceeds the preset differential current threshold and the ratio of differential current to braking current exceeds the preset proportional coefficient, but the total differential allow flag is set to prohibition flag 0, it indicates that the current T zone is in a steady-state operation with multiple branches under stable load. The excessive differential current at this time is not caused by a fault, but is a false differential current formed by the accumulation of current transformer transmission deviation, secondary sampling error, and steady-state load imbalance in multiple branches. It does not have fault characteristics. Therefore, the differential protection is prohibited from performing protection actions, and the protection output is reliably blocked.

[0098] It should be understood that this embodiment, based on the electrical criteria of traditional ratio-controlled differential protection, introduces a global differential allowance flag for operating condition verification, thus solving the technical defect of traditional T-zone differential protection in being unable to distinguish between steady-state false differential current and fault real differential current. Through a two-layer check mechanism of accurately identifying fault characteristics with electrical quantities and discerning operating status with operating condition flags, it ensures both the sensitivity and speed of differential protection operation under fault conditions, and effectively blocks false tripping caused by false differential current under normal steady-state operating conditions, greatly improving the operational reliability and operating condition adaptability of T-zone differential protection. This step, together with the aforementioned steps, forms a complete closed-loop adaptive differential protection logic, which can be implemented solely through software algorithms without adding hardware, demonstrating strong engineering applicability and high promotional value.

[0099] It is understood that the embodiments of this application provide a T-zone differential protection method, which is applicable to multi-branch differential protection scenarios in which multiple branches converge at the same electrical node to form a T-type topology. It can adapt to branch switching, branch no-load and steady-state load operation conditions, and realize adaptive control of differential protection to prevent false tripping and maintain sensitivity. Specifically, it includes the following steps.

[0100] First, the differential allowance flag of the current transformer configured in each branch of Zone T is obtained, as well as the current differential operation mode of the differential protection device in Zone T. Zone T is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node. Each branch is equipped with a current transformer for real-time acquisition of the branch's three-phase current signals. This step independently determines the differential allowance flag corresponding to each current transformer using a phase-by-phase current cycle change abrupt change criterion and a three-phase no-current state continuity criterion. Simultaneously, based on the branch switch position status in Zone T, the differential protection device is adaptively identified as currently operating in either a two-sided differential mode or a three-sided differential mode, completing a comprehensive perception of the topology's operating status and the electrical conditions of each branch.

[0101] Secondly, based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device, the overall differential allowance flag of zone T is determined. When the differential protection is in the two-sided differential operation mode, the overall differential allowance flag is set to allow only when the differential allowance flags of the current transformers corresponding to the two branches are both allowed. If any branch is in the steady-state prohibited state, the differential is blocked as a whole. When the differential protection is in the three-sided differential operation mode, it adapts to two normal topology conditions: full branch energized operation and single branch unloaded operation. Under the condition that the number of no-current branches is zero and at least two branches are allowed, or single branch is unloaded and the remaining two branches are allowed, the overall differential allowance flag is opened. The overall differential logic is blocked under other complex abnormal conditions, so as to achieve accurate identification of the full differential enable state of the multi-branch zone T.

[0102] Next, based on the current differential operation mode of the differential protection device, the differential current and braking current in zone T are determined. In the two-sided differential operation mode, the current data of the out-of-operation branch is discarded, and the vector sum of the currents of the first and second branches is used as the differential current, while the sum of the amplitudes of the two currents is used as the braking current. In the three-sided differential operation mode, the currents of the first, second, and third branches are used uniformly in the calculation, with the vector sum of the three currents used to construct the differential current and the sum of the amplitudes of the three currents used to construct the braking current. By using an adaptive current calculation model that matches the operation mode, the accuracy of differential electrical quantity calculations under different topologies is ensured, avoiding zero-drift sampling of the out-of-operation branch and the introduction of false differential currents by electromagnetic interference.

[0103] Finally, based on the total differential allowance flag, differential current, and braking current, a comprehensive determination is made as to whether to control the differential protection device to perform protection actions. When the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, and the total differential allowance flag is set to allow, it is determined that the current electrical anomaly is caused by a real fault or effective transient disturbance within the zone, and the differential protection device is controlled to perform protection actions to quickly isolate the fault area. When the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, but the total differential allowance flag is set to prohibit, it is determined that the current electrical quantity exceeding the limit is a false differential current formed by the accumulation of transmission errors of multiple branch current transformers, sampling deviations, and steady-state load imbalances, and is not a real power grid fault. Therefore, the differential protection device is not controlled to perform protection actions, achieving reliable protection against false tripping under steady-state conditions.

[0104] It should be understood that this embodiment, while ensuring the sensitivity and reliability of the differential protection for faults within the zone, greatly improves the steady-state anti-interference capability under normal operating conditions in the T zone. The overall logic is implemented based on software algorithms, requiring no hardware modification, and is adaptable to various T zone projects, demonstrating significant value for engineering application and promotion.

[0105] 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 this application.

[0106] Corresponding to the T-zone differential protection method in the above embodiment, Figure 3 A schematic diagram of a T-zone differential protection device according to an embodiment of this application is shown. For ease of explanation, only the parts related to the embodiment of this application are shown.

[0107] Reference Figure 3 The T-zone differential protection device 3 in this embodiment includes: The acquisition module 31 is used to acquire the differential allow flag of the current transformer configured in each branch in the T zone, as well as the current differential operation mode of the differential protection device in the T zone. The T zone is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node.

[0108] The determination module 32 is used to determine the total differential permission flag of zone T based on the differential permission flag of each current transformer and the current differential operation mode of the differential protection device.

[0109] The calculation module 33 is used to determine the differential current and braking current in zone T based on the current differential operation mode of the differential protection device.

[0110] The judgment module 34 is used to determine whether to control the differential protection device to perform protection actions based on the total differential allowance flag, differential current and braking current.

[0111] Furthermore, the acquisition module 31 includes: The first condition confirmation submodule is used to calculate the current cycle change of the current transformer configured for each branch on a phase-by-phase basis. If the cycle change corresponding to a preset number of consecutive sampling points is greater than a preset change threshold, it is determined that the current transformer meets the change start condition.

[0112] The second condition confirmation submodule is used to monitor the three-phase current amplitude of the current transformer configured in each branch in real time. If the three-phase no-current state of the current transformer continues for a preset time, it is determined that the current transformer is in a state of no current in all three phases.

[0113] The first flag confirmation submodule is used to determine the differential allowance flag of the current transformer as an allowance flag when the current transformer meets the change start condition or is in a state where all three phases are without current.

[0114] The second flag confirmation submodule is used to determine the differential allow flag of the current transformer as the prohibition flag when the current transformer does not meet the change start condition and is not in a state where all three phases are without current.

[0115] Furthermore, the multiple branches include a first branch configured with a first current transformer, a second branch configured with a second current transformer, and a third branch configured with a third current transformer.

[0116] The acquisition module 31 includes: The first operating mode determination submodule is used to determine the current differential operating mode of the differential protection device as the three-sided differential operating mode when the switch of the third branch is in the closed state.

[0117] The second operating mode determination submodule is used to determine the current differential operating mode of the differential protection device as the two-sided differential operating mode when the switch of the third branch is in the open state.

[0118] Furthermore, module 32 includes: The first overall flag determination unit is used to determine the overall differential allowance flag of zone T as the allowance flag when the current differential operation mode of the differential protection device is the two-sided differential operation mode, and if both the differential allowance flags of the first current transformer and the second current transformer are allowance flags. Also, The second overall flag determination unit is used to determine that the overall differential allow flag of zone T is a prohibition flag if the differential allow flag of the first current transformer or the differential allow flag of the second current transformer is a prohibition flag.

[0119] The third overall flag determination unit is used to determine the overall differential allowance flag of zone T as allowable when the current differential operation mode of the differential protection device is three-sided differential operation mode, and if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0, and there are at least two current transformers whose differential allowance flags are allowable flags. The fourth overall flag determination unit is used to determine the overall differential allowable flag of zone T as an allowable flag if the number of current transformers in the first, second and third current transformers that are all in a state of no current in all three phases is 1, and the differential allowable flags of the remaining two current transformers are both allowable flags.

[0120] The fifth overall flag determination unit is used to determine the overall differential allowance flag of zone T as a prohibition flag if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0 and the number of current transformers with allowance flags is less than two, or if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 1 and the differential allowance flag of at least one of the remaining two current transformers is a prohibition flag.

[0121] Furthermore, the computing module 33 includes: The first calculation submodule is used to, when the current differential operation mode of the differential protection device is the two-sided differential operation mode, take the vector sum of the current of the first branch and the current of the second branch as the differential current of zone T, and take the sum of the magnitudes of the current of the first branch and the current of the second branch as the braking current of zone T.

[0122] The second calculation submodule is used to, when the current differential operation mode of the differential protection device is three-sided differential operation mode, take the vector sum of the currents of the first branch, the second branch, and the third branch as the differential current of zone T. It also takes the sum of the magnitudes of the currents of the first branch, the second branch, and the third branch as the braking current of zone T.

[0123] Furthermore, the judgment module 34 includes: The execution submodule is used to control the differential protection device to perform protection actions when the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, and the total differential allowance flag is the allowance flag.

[0124] The prohibition submodule is used to prevent the differential protection device from performing protection actions when the differential current is greater than the preset differential current threshold, the ratio of differential current to braking current is greater than the preset proportional coefficient, but the total differential allow flag is the prohibition flag.

[0125] It should be noted that the information interaction and execution process between the modules in the aforementioned T-zone differential protection device 3 are based on the same concept as the method embodiment of this application. For details on their specific functions and technical effects, please refer to the method embodiment section, which will not be repeated here.

[0126] This application also provides a terminal device, such as... Figure 4 As shown, Figure 4 This is a schematic diagram of the structure of a terminal device provided in an embodiment of this application. (Refer to...) Figure 4 The terminal device 4 in this embodiment includes a memory 41, a processor 42, and a computer program stored in the memory 41 and executable on the processor 42. When the processor 42 executes the computer program, it implements the steps in the T-zone differential protection method embodiment described above.

[0127] This application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, can implement the steps in the above-described method embodiments.

[0128] This application provides a computer program product that, when run on a mobile terminal, enables the mobile terminal to implement the steps described in the various method embodiments.

[0129] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of this application can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying the computer program code to a photographic device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks.

[0130] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0131] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0132] In the embodiments provided in this application, it should be understood that the disclosed apparatus / network devices and methods can be implemented in other ways. For example, the apparatus / network device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0133] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0134] The technical features of the various embodiments described above in this application can be combined arbitrarily without conflict. For the sake of brevity, this specification does not describe all possible combinations, but as long as these combinations do not violate the technical spirit of this application, they should all be considered within the scope of this application. Based on the content disclosed in this application, those skilled in the art can reasonably combine, delete, or replace the technical features of the above embodiments according to actual needs, and such modifications and variations all fall within the protection scope of this application.

[0135] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application, and should all be included within the protection scope of this application.

Claims

1. A T-zone differential protection method, characterized in that, include: Obtain the differential allow flag of the current transformer configured in each branch in zone T, and the current differential operation mode of the differential protection device in zone T, wherein zone T is a T-shaped topology electrical area formed by multiple branches converging at the same electrical node; The total differential allowance flag of zone T is determined based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device; Based on the current differential operation mode of the differential protection device, determine the differential current and braking current in zone T; Based on the total differential allowance flag, the differential current, and the braking current, determine whether to control the differential protection device to perform a protection action.

2. The T-zone differential protection method as described in claim 1, characterized in that, Obtain the differential allowance flag of the current transformer configured for each branch in zone T, including: The current frequency change of the current transformer configured for each branch is calculated phase by phase. If the frequency change corresponding to a preset number of consecutive sampling points is greater than a preset change threshold, the current transformer is determined to meet the change start condition. The three-phase current amplitude of the current transformer configured in each branch is monitored in real time. If the three-phase no-current state of the current transformer continues for a preset time, it is determined that the current transformer is in a state of no current in all three phases. When the current transformer meets the change start condition, or is in a state where all three phases are without current, the differential allowable flag of the current transformer is determined to be an allowable flag. When the current transformer does not meet the change-of-current start-up conditions and is not in a state where all three phases are without current, the differential allow flag of the current transformer is determined to be a prohibition flag.

3. The T-zone differential protection method as described in claim 2, characterized in that, The plurality of branches include a first branch configured with a first current transformer, a second branch configured with a second current transformer, and a third branch configured with a third current transformer. Obtaining the current differential operation mode of the differential protection device in zone T includes: When the switch of the third branch is in the closed state, the current differential operation mode of the differential protection device is determined to be the three-sided differential operation mode; When the switch of the third branch is in the open state, the current differential operation mode of the differential protection device is determined to be the two-sided differential operation mode.

4. The T-zone differential protection method as described in claim 3, characterized in that, The step of determining the total differential allowance flag of zone T based on the differential allowance flag of each current transformer and the current differential operation mode of the differential protection device includes: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, if both the differential allowance flag of the first current transformer and the differential allowance flag of the second current transformer are the allowance flags, then the total differential allowance flag of zone T is determined to be the allowance flag; and, If the differential allow flag of the first current transformer or the differential allow flag of the second current transformer is the prohibition flag, then the total differential allow flag of the T zone is determined to be the prohibition flag; When the current differential operation mode of the differential protection device is the three-sided differential operation mode, if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0, and there are at least two current transformers whose differential allowance flag is the allowance flag, then the total differential allowance flag of the T zone is determined to be the allowance flag; and, If the number of current transformers in the first, second, and third current transformers that are all in a three-phase no-current state is 1, and the differential allowance flags of the remaining two current transformers are both the allowance flag, then the total differential allowance flag of the T-zone is determined to be the allowance flag; and, If the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 0 and the number of current transformers with the permission flag is less than two, or if the number of current transformers in the first, second, and third current transformers that are all in a state of no current in all three phases is 1 and the differential permission flag of at least one of the remaining two current transformers is the prohibition flag, then the total differential permission flag of the T-zone is determined to be the prohibition flag.

5. The T-zone differential protection method as described in claim 4, characterized in that, The step of determining the differential current and braking current in zone T based on the current differential operation mode of the differential protection device includes: When the current differential operation mode of the differential protection device is the two-sided differential operation mode, the vector sum of the current of the first branch and the current of the second branch is taken as the differential current of the T zone; and the sum of the magnitudes of the current of the first branch and the current of the second branch is taken as the braking current of the T zone. When the current differential operation mode of the differential protection device is the three-sided differential operation mode, the vector sum of the current of the first branch, the current of the second branch, and the current of the third branch is taken as the differential current of the T zone; and the sum of the amplitudes of the current of the first branch, the current of the second branch, and the current of the third branch is taken as the braking current of the T zone.

6. The T-zone differential protection method as described in claim 5, characterized in that, The step of determining whether to control the differential protection device to perform a protection action based on the total differential allowance flag, the differential current, and the braking current includes: When the differential current is greater than a preset differential current threshold, the ratio of the differential current to the braking current is greater than a preset proportional coefficient, and the total differential allowance flag is the allowance flag, the differential protection device is controlled to perform a protection action. When the differential current is greater than the preset differential current threshold, the ratio of the differential current to the braking current is greater than the preset proportional coefficient, but the total differential allow flag is the prohibition flag, the differential protection device is not controlled to perform protection action.

7. A T-zone differential protection device, characterized in that, include: The acquisition module is used to acquire the differential allow flag of the current transformer configured in each branch in the T zone, as well as the current differential operation mode of the differential protection device in the T zone, wherein the T zone is a T-shaped topology electrical area formed by the convergence of the multiple branches at the same electrical node; The determination module is used to determine the total differential permission flag of the T zone based on the differential permission flag of each current transformer and the current differential operation mode of the differential protection device; The calculation module is used to calculate the differential current and braking current of the T-zone; The judgment module is used to determine whether to control the differential protection device to perform a protection action based on the total differential allowance flag, the differential current, and the braking current.

8. A terminal device, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as claimed in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method as described in any one of claims 1 to 6.

10. A computer program product, characterized in that, Includes a computer program, which, when run, causes the method as described in any one of claims 1 to 6 to be performed.

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