Fault protection method and device under double-branch connection mode of transformer

Abstract

The application discloses a fault protection method and device under a double-branch connection mode of a transformer. The fault protection method comprises the following steps: when a fault occurs in at least one branch structure, the action states of interval devices, backup protection devices and an operating grounding transformer are controlled according to a preset tripping matrix; if there is a loss-of-voltage bus, the action identification of the backup protection devices is valued according to the action information of the backup protection devices, and the action identification of the grounding transformer is valued according to the action information of the grounding transformer; the fault identification of each interval switch is valued according to the action information of each interval device and the action information of each interval switch in the branch structure where the loss-of-voltage bus is located; the fault position is determined according to the action identification of the backup protection devices, the action identification of the grounding transformer and the fault identification of the interval switch, the fault is isolated, and the power supply of a non-fault part is restored. The application can automatically determine the fault point, so as to restore the power supply of the non-fault point as soon as possible, and improve the power supply reliability of a distribution network.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a fault protection method and device for a transformer with a double-branch connection. Background Technology

[0002] With the rapid growth of electricity load, the scale of distribution networks is constantly expanding and extending. As the load in distribution networks becomes increasingly heavy, the requirements for power supply reliability are also increasing. To reduce the transformer's capacity-to-load ratio, a dual-branch structure is being adopted on the low-voltage side of the main transformer, using dual-branch switches to supply power to two bus sections. Existing fault protection methods typically only include the design of the timing coordination of various levels of protection devices, but do not include automatic fault location. In a branch structure, after a bus loses voltage due to protection device operation, operators must immediately go to the station to check the fault location and cooperate with the dispatch center to collect various protection actions and switch change timing information to determine the fault location. Currently, under existing fault protection schemes, the determination of the fault location after protection action relies solely on operators comparing various collected information, which is time-consuming, inconvenient, and its accuracy is greatly affected by the subjective factors of maintenance personnel. Furthermore, in the existing fault protection scheme, the first time limit action of the zero-sequence current protection of the grounding transformer does not distinguish between the busbars. When a fault occurs, the busbars in both branches will be disconnected simultaneously without difference. Therefore, the longer the fault point is determined, the slower the power supply to the non-faulty busbars and non-faulty lines will be restored, which will cause unnecessary power outages to non-faulty points for a long time and affect the reliability of the distribution network power supply. Summary of the Invention

[0003] This invention provides a fault protection method and device for transformers with dual-branch connection, so as to realize the automatic determination of fault points in the branch structure of the distribution network, thereby restoring power supply to non-fault points as soon as possible and improving the reliability of power supply in the distribution network.

[0004] In a first aspect, embodiments of the present invention provide a fault protection method for a transformer with a dual-branch connection, wherein the low-voltage side of the transformer is connected to two branch structures; each branch structure includes: a busbar, a low-voltage branch switch, a grounding transformer, and a bay device; the low-voltage branch switch is connected between the low-voltage side of the transformer and the busbar; the grounding transformer is connected to the busbar; at least one line is led out from the busbar, and each line is connected to a bay device in a one-to-one correspondence, the line being connected to the busbar via a bay switch, and the bay device being used to control the bay switch to trip; the transformer includes two backup protection devices, each corresponding to one of the two branch structures, and the backup protection devices being used to control the low-voltage branch switch to trip; wherein, during the operation of the two branch structures, one grounding transformer is in operation, and the other grounding transformer is in hot standby mode;

[0005] The fault protection method for the transformer with dual-branch connection includes:

[0006] When a fault occurs in at least one of the branch structures, the operating status of each of the interval devices, each of the backup protection devices and the operating grounding transformer is controlled according to a preset tripping matrix.

[0007] If there is an undervoltage busbar, the action identifier of the backup protection device is assigned a value according to the action information of the backup protection device, and the action identifier of the grounding transformer is assigned a value according to the action information of the grounding transformer.

[0008] The fault identifier of each of the interval switches is assigned a value based on the operation information of each of the interval devices and the operation information of each of the interval switches in the branch structure where the undervoltage busbar is located;

[0009] The fault location is determined based on the operation indicators of the backup protection equipment, the operation indicators of the grounding transformer, and the fault indicators of the interval switch. The fault is then isolated and power supply to the non-faulty parts is restored.

[0010] Optionally, the preset trip matrix includes:

[0011] When the operating grounding transformer detects a branch structure with a grounding fault, the zero-sequence protection of the operating grounding transformer is controlled to operate for a time limit, causing the operating grounding transformer to issue a first action signal, thereby causing the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located to trip.

[0012] If the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located trips, and the branch structure where the operating grounding transformer has detected a grounding fault still exists, then the zero-sequence protection of the operating grounding transformer is controlled to operate under time-limited conditions, causing the operating grounding transformer to issue a second action signal, thereby causing the low-voltage branch switch in the branch structure where the operating grounding transformer is located to trip.

[0013] Optionally, the preset trip matrix further includes:

[0014] When at least one of the backup protection devices reacts to a phase-to-phase fault in its corresponding branch structure, the backup protection device of the branch structure where the phase-to-phase fault is located is controlled to perform a time-limited overvoltage overcurrent operation, causing the backup protection device to issue a third action signal, thereby causing the low-voltage branch switch of the branch structure where the phase-to-phase fault is located to trip.

[0015] When at least one of the interval devices reports a fault in the line it is connected to, the interval device that reports the fault issues sends a fourth action signal, thereby causing the interval switch of the line connected to the faulty interval device to trip.

[0016] Optionally, assigning a value to the action identifier of the backup protection device based on the action information of the backup protection device includes: if the backup protection device does not activate during the overvoltage overcurrent time limit, then assigning 0 to the action identifier of the backup protection device; if the backup protection device activates during the overvoltage overcurrent time limit, then assigning 1 to the action identifier of the backup protection device.

[0017] The operation flag of the grounding transformer is assigned a value based on the operation information of the grounding transformer, including: if neither the zero-sequence protection time limit one nor the zero-sequence protection time limit two of the grounding transformer operates, the operation flag of the grounding transformer is set to 0; if the zero-sequence protection time limit one of the grounding transformer operates, but the zero-sequence protection time limit two of the grounding transformer does not operate, the operation flag of the grounding transformer is set to 1, and the time of the zero-sequence protection time limit one of the grounding transformer is recorded as the operation time of the grounding transformer; if the zero-sequence protection time limit two of the grounding transformer operates, the operation flag of the grounding transformer is set to 1, and the time of the zero-sequence protection time limit two of the grounding transformer is recorded as the operation time of the grounding transformer.

[0018] Assigning a fault identifier to the interval switch based on the operation information of the interval device and the operation information of the interval switch includes: if the interval device issues a fourth operation signal and the corresponding interval switch operation information includes position information and protection operation return information, then the fault identifier of the interval switch is assigned 0; if the interval device issues a fourth operation signal, but the corresponding interval device operation information does not include position information and / or protection operation return information, then the fault identifier of the interval switch is assigned 1.

[0019] Optionally, the fault location is determined based on the operation indicator of the backup protection device, the operation indicator of the grounding transformer, and the fault indicator of the interval switch, including:

[0020] When the action flag of the backup protection device is 1, the relevant equipment action flag of the bus in the branch structure corresponding to the backup protection device is assigned 1;

[0021] When the operation flag of the grounding transformer is 1 and the operation time of the grounding transformer is zero-sequence protection time limit, the operation flag of the relevant equipment on the bus connected to the grounding transformer is set to 1;

[0022] When the operation flag of the grounding transformer is 1 and the operation time of the grounding transformer is the zero-sequence protection time limit, the operation flag of the relevant equipment on the bus that is not directly connected to the grounding transformer will be set to 1.

[0023] When the relevant equipment action flag of the undervoltage bus is 1, and the fault flags of all bay switches in the branch structure where the undervoltage bus is located are 0, the fault is located on the undervoltage bus.

[0024] When the relevant equipment operation flag of the undervoltage busbar is 1, and the fault flag of at least one compartment switch in the branch structure where the undervoltage busbar is located is 1, then the fault is located on the line where the compartment switch with fault flag 1 is located.

[0025] Optionally, determining the fault location based on the operation indicator of the backup protection device, the operation indicator of the grounding transformer, and the fault indicator of the interval switch further includes:

[0026] If there is an undervoltage bus, and the operation indicators of all backup protection devices and all grounding transformers are 0, then the fault is located in the upstream power supply of the branch structure or the voltage transformer connected to the undervoltage bus.

[0027] Optionally, the fault identifier is a failure to operate identifier. When the interval device issues a fourth action signal, but the corresponding interval switch action information does not include the position information, the failure to operate identifier of the interval switch is assigned 1.

[0028] Alternatively, the fault identifier is a slow separation identifier. When the interval device issues a fourth action signal, the action information of the interval switch includes separation information, but the separation time of the interval switch is greater than a preset time threshold, the slow separation identifier of the interval switch is assigned 1.

[0029] Alternatively, the fault identifier is an unisolated fault identifier. When the interval device issues a fourth action signal, the action information of the interval switch includes squaring information, the squaring time of the interval switch is less than the preset time threshold, but the action information of the interval switch does not include protection action return information, the unisolated fault identifier of the interval switch is assigned 1.

[0030] Optionally, the interval device reports a total accident signal after it is activated;

[0031] The process of obtaining the interval time of the interval switch includes:

[0032] Search for the time when the action signal of the interval device is reported within the first preset time period, and record the first time when the action signal of the interval device is reported within the first preset time period as the action time of the interval device; wherein, the first preset time period includes the time when the total accident signal is reported;

[0033] If there is reclosing information of the interval switch within the first preset time period, then the last action signal reporting time of the interval device within the first preset time period is recorded as the reclosing action time of the interval device.

[0034] Search for the reporting time of the interval switch's position signal within the second preset time period;

[0035] If at least one segment signal reporting time is found, the time difference between the first segment signal reporting time within the second preset time period and the start time of the second preset time period is recorded as the segment time of the interval switch; wherein, the start time of the second preset time period is the action time or the action time after overlap.

[0036] Optionally, after controlling the operating status of each of the interval devices, each of the backup protection devices, and the operating grounding transformer according to the preset tripping matrix, the method further includes:

[0037] If there is no undervoltage bus, the operation information of all bay devices and all bay switches in the two branch structures is obtained, and the health status of each bay device and each bay switch is determined based on the operation information of each bay device and each bay switch.

[0038] Secondly, embodiments of the present invention also provide a fault protection device for a transformer with a dual-branch connection, comprising:

[0039] The protection action control module is used to control the operation status of each bay device, each backup protection device and the operating grounding transformer according to a preset trip matrix when a fault occurs in at least one of the branch structures.

[0040] The action identifier assignment module is used to assign an action identifier value to the backup protection device according to the action information of the backup protection device when there is an undervoltage bus, and to assign an action identifier value to the grounding transformer according to the action information of the grounding transformer.

[0041] The fault identification assignment module is used to assign fault identification values ​​to each of the bay switches based on the operation information of each of the bay devices and the operation information of each of the bay switches in the branch structure where the undervoltage bus is located.

[0042] The fault location module is used to determine the fault location based on the operation identifier of the backup protection device, the operation identifier of the grounding transformer, and the fault identifier of the interval switch, isolate the fault, and restore power supply to the non-faulty part.

[0043] The fault protection method for a transformer with a dual-branch connection provided in this invention involves assigning values ​​to characteristic identifiers such as the action identifier of the backup protection device, the action identifier of the grounding transformer, and the fault identifier of the bay switch based on the action information of each protection device and the action information of the switch, after the fault is located according to the aforementioned characteristic identifiers. Compared with the prior art, which relies on operators to collect and compare various information to determine the fault point, the fault method provided in this invention can achieve automatic fault location through various characteristic identifiers, thereby reducing the risk of human subjective judgment errors. Furthermore, this method can quickly determine the fault location, providing operators with the conditions to quickly isolate the fault and restore power supply to the non-faulty parts, minimizing the power outage time at non-faulty points and protecting the electrical load. Therefore, compared with the prior art, this invention can automatically determine the fault point in the branch structure of the distribution network, thereby quickly restoring power supply to non-faulty points and improving the reliability of the distribution network power supply.

[0044] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of a transformer with a double-branch connection provided in an embodiment of the present invention;

[0047] Figure 2 This is a flowchart illustrating a fault protection method for a transformer with a dual-branch connection provided in an embodiment of the present invention.

[0048] Figure 3 This is a flowchart illustrating a fault protection method for a transformer with a dual-branch connection provided in an embodiment of the present invention.

[0049] Figures 4-8 This is a flowchart illustrating another fault protection method for a transformer with a dual-branch connection provided in an embodiment of the present invention.

[0050] Figure 9 This is a schematic diagram of the structure of a fault protection device for a transformer with a dual-branch connection method provided in an embodiment of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0053] This invention provides a fault protection method for a transformer with a double-branch connection. This embodiment is applicable to the fault handling and recovery needs of the double-branch low-voltage side of the main transformer in the distribution network. The method can be executed by a fault protection device for the transformer with a double-branch connection. The fault protection device for the transformer with a double-branch connection can be implemented in hardware and / or software. The fault protection device for the transformer with a double-branch connection can be configured in the controller or other electronic equipment in the distribution network dispatch center.

[0054] To better explain the fault protection method provided in the embodiments of the present invention, the transformer double-branch structure will be described first. Figure 1 This is a schematic diagram of a transformer with a double-branch connection according to an embodiment of the present invention. See also... Figure 1For example, transformer T can be a main transformer in a distribution network, which may include a high-voltage side, a medium-voltage side, and a low-voltage side. Here, "transformer" refers to the transformer body and the various protection devices configured within it, including high-voltage side protection, medium-voltage side protection, and low-voltage side protection. The low-voltage side of transformer T is connected to two branch structures 10. The protection devices configured on the transformer include two backup protection devices, each corresponding one-to-one with one of the two branch structures, each used to implement a low-voltage backup protection function for one branch structure. Each branch structure 10 includes: a busbar, a low-voltage branch switch, a grounding transformer, and bay equipment. The low-voltage branch switch is connected between the low-voltage side of transformer T and the busbar; the grounding transformer is connected to the busbar. Both the grounding transformer and the transformer's backup protection devices can serve as busbar-related protection devices. When the protection time limit of the grounding transformer and the backup protection devices is activated, the activation signals issued can be used to trip the corresponding low-voltage branch switch, thereby disconnecting the busbar connected to the low-voltage branch switch and causing the busbar to lose voltage. For example, different time limits of the grounding transformer are used to control the switching states of different low-voltage branch switches (e.g., controlling the low-voltage branch switch to trip); backup protection devices are used to control the switching states of the low-voltage branch switches in their corresponding branch structures (e.g., controlling the low-voltage branch switch to trip). At least one line (outgoing line) is led out from each busbar, and each line is connected to each bay device in a one-to-one correspondence. Each line is connected to the busbar through a bay switch (not shown in the figure). The bay device, as a line-related protection device, is used to control the switching states of the bay switches. For example, when the protection time limit of a certain bay device operates, its action signal can be used to control the bay switch in operation on the line connected to that bay device to trip, thereby disconnecting the line and causing it to lose voltage. For example, the bay device can be an auxiliary device such as a capacitor.

[0055] Figure 1 Two bay devices are provided exemplary in each branch structure 10, but the number of bay devices is not intended to limit the invention. In practical applications, the number of lines connected to the busbar can be determined according to load requirements, thereby determining the number of bay devices. Specifically, as shown... Figure 1As shown, the first branch structure 11 includes a first busbar L1, a first low-voltage branch switch 502, a first grounding transformer 507, a first first bay device F21, and a second first bay device F23. The second branch structure 12 includes a second busbar L2, a second low-voltage branch switch 506, a second grounding transformer 508, a first second bay device F22, and a second second bay device F24. Exemplarily, the first backup protection device (not shown in the figure) of transformer T corresponds to the first branch structure 11 and is used to control the first low-voltage branch switch 502; the second backup protection device (not shown in the figure) of transformer T corresponds to the second branch structure 12 and is used to control the second low-voltage branch switch 506.

[0056] It should be noted that the various devices mentioned here (including transformer T, grounding transformer, and bay equipment) refer to the entire equipment, including both primary equipment (the operating device itself connected in the line) and secondary equipment (protective devices used to receive data, process data, generate and transmit operating signals, or communicate and exchange data with other equipment). For example, the busbar in branch structure 10 can be a 10kV busbar, and both grounding transformers can be 10kV grounding transformers.

[0057] In the dual-branch wiring configuration, following the principle that the same system has only one grounding point at any given time, during the operation of the two branch structures 10, one grounding transformer is in operation while the other is in hot standby mode. That is, when the first grounding transformer 507 is in operation, the second grounding transformer 508 is in hot standby mode; when the second grounding transformer 508 is in operation, the first grounding transformer 507 is in hot standby mode.

[0058] As described in the background section, electricity load is currently growing rapidly. However, existing phased projects often consider commissioning a single-branch main transformer in the first phase, with one 10kV busbar on the low-voltage side, and then expanding to a double-branch main transformer in the second phase, supporting two 10kV busbars. Due to the rapid growth of 10kV load, relying solely on a single-branch main transformer supporting one 10kV busbar is far from sufficient to meet the increasing load demand. Constrained by site and funding limitations, the second-phase expansion project often takes many years to commence. In this situation, when a planned power outage maintenance is required on the busbar in the single-branch structure, all 10kV lines need to be switched, which is difficult; lines that cannot be switched need to be shut down, affecting power supply continuity. Therefore, it is advisable to first commission a double-branch main transformer on the low-voltage side in the first phase, operating it with two 10kV busbars respectively; the second phase can then expand with a single-branch main transformer.

[0059] The following is in conjunction with the above. Figure 1 The transformer dual-branch structure given in the paper is used to explain the fault protection method. Figure 2This is a flowchart illustrating a fault protection method for a transformer with a dual-branch connection, provided in an embodiment of the present invention. See also... Figure 2 The fault protection method includes the following steps:

[0060] S110. When a fault occurs in at least one branch structure, control the operation status of each bay device, each backup protection device and the operating grounding transformer according to the preset trip matrix.

[0061] According to the type of fault, the faults that may occur in the branch structure include grounding faults and phase-to-phase faults; according to the location of the fault, the busbars and lines in the branch structure may experience all of the above types of faults.

[0062] The preset trip matrix includes the operating strategies of each protection device under various fault conditions, specifically including the correspondence between each trip output and the trip setting time. Once the wiring of the system's external trip circuit is configured, the internal logic set in the trip matrix can control each protection function logic to activate the corresponding output relay, thereby disconnecting the bus or line from the system by opening the switches of each protection device. For example, based on the preset trip matrix, when a certain protection time limit of the grounding transformer operates, the operating signal issued by its secondary equipment can be used to control the tripping of a certain transformer branch switch.

[0063] Each protection device can be uniformly controlled by the controller according to the preset trip matrix; alternatively, the controller can first send the protection logic related to each protection device in the preset trip matrix to each protection device. When a protection device reacts to the fault by receiving changes in electrical quantities, it can determine whether its various protection time limits should be activated according to the preset protection logic. Among them, electrical quantities can include voltage and current, which are collected in real time by electrical quantity acquisition devices such as voltage transformers (PT) and current transformers installed at the power grid site.

[0064] For example, a ground fault can manifest as a zero-sequence current or zero-sequence voltage in the system, which can be detected and responded to by the secondary equipment of the grounding transformer through the acquisition of electrical quantities. When a phase-to-phase fault occurs, the fault current increases compared to the normal current. Phase-to-phase faults can be detected and responded to by the secondary equipment on the low-voltage side of the transformer (i.e., backup protection equipment) through the acquisition of electrical quantities. The secondary equipment of the bay equipment can detect and respond to various faults in each line through the acquisition of electrical quantities.

[0065] In the preset trip matrix, the operating time of each protection delay of the line-related protection equipment (bay equipment) can be set to be earlier than that of each protection delay of the bus-related protection equipment (backup protection equipment or grounding transformer). In this way, when a line fault occurs, the bay equipment first sends an operating signal. If the bay switch is normal, it can correctly operate to disconnect the faulty line. The bus-related protection equipment may not operate because the protection time delay is not met, and the low-voltage branch switch does not need to trip, thus avoiding unnecessary power outages on the bus. However, if the bay switch itself fails and cannot disconnect the faulty line, the protection of the bus-related protection equipment will then cascade, tripping the low-voltage branch switch and disconnecting the bus. This prevents the bus from operating in a faulty state for an extended period. Once the fault location is subsequently determined, the faulty line can be disconnected, and power supply to the bus and normal lines can be restored as quickly as possible, ensuring power supply reliability.

[0066] S120. If there is an undervoltage busbar, the action flag of the backup protection device shall be assigned a value according to the action information of the backup protection device, and the action flag of the grounding transformer shall be assigned a value according to the action information of the grounding transformer.

[0067] Once the protection devices have completed their protection actions, the controller can enter the fault location judgment process in order to accurately locate the fault and assist staff in cutting off the fault and restoring power to the non-faulty parts of the system as soon as possible.

[0068] The main idea of ​​this fault location process is to: extract multiple feature identifiers related to fault location determination; combine the limited action signals issued by each protection device, as well as the change information of each switch that responds to the above action signals, to assign values ​​to each feature identifier; and then determine the fault point based on the values ​​of each feature identifier.

[0069] The initial value of each feature identifier (or the value representing the normal operation of the system) can be 0. After the identifier setting condition is met, the feature identifier can be assigned a value of 1. Feature identifiers may include the action identifiers of each protection device, the fault identifiers of each switch, and the status identifiers of the bus and lines (such as whether there is a voltage loss).

[0070] For example, the operation information of the grounding transformer may include whether the protection time limit of the grounding transformer has been activated, and the operation information of the backup protection device may include whether the protection time limit of the backup protection device has been activated. For instance, when a certain time limit of the grounding transformer is activated, causing the secondary equipment of the grounding transformer to issue a corresponding operation signal, the controller can set the operation flag of the grounding transformer to 1.

[0071] S130. Assign fault identifiers to each bay switch based on the operation information of each bay device and the operation information of each bay switch in the branch structure where the undervoltage busbar is located.

[0072] The operation information of the bay device may include whether the bay device has issued an operation signal; the operation information of the bay switch may include whether the bay switch has changed position and the time of the change position. For example, the operation signal issued by the secondary device in the bay device is used to control the bay switch in the line it is connected to to trip. If the bay device issues an operation signal, but the operation information of the corresponding bay switch does not include the protection operation return information of its successful tripping, it may indicate that the bay switch is faulty, and the controller can set the fault flag of the bay switch to 1.

[0073] S140. Determine the fault location based on the operation indicators of the backup protection equipment, the operation indicators of the grounding transformer, and the fault indicators of the interval switch, isolate the fault, and restore power supply to the non-faulty parts.

[0074] Specifically, this step can be as follows: the controller assigns values ​​to the relevant equipment action flags of each busbar based on the action flags of the backup protection equipment and the grounding transformer; then, it determines the fault location based on the relevant equipment action flags and the fault flags of each bay switch. For example, when the relevant equipment action flag is 1, it indicates that the busbar has been disconnected due to the action of the busbar-related protection equipment. If the fault flags of each bay switch are all 0, it proves that each bay switch can normally disconnect the faulty line. If the busbar-related protection equipment operates when all bay switches are normal, it indicates a fault in the busbar itself. However, when the fault flag of a bay switch is 1, it indicates that the bay switch cannot disconnect the faulty line, causing the busbar-related protection equipment to overstep its cascading action and disconnect the busbar. In this case, the fault point is located on the line where the bay switch with fault flag 1 is located.

[0075] The fault protection method for a transformer with a dual-branch connection provided in this invention involves assigning values ​​to characteristic identifiers such as the action identifier of the backup protection device, the action identifier of the grounding transformer, and the fault identifier of the bay switch based on the action information of each protection device and the action information of the switch, after the fault is located according to the aforementioned characteristic identifiers. Compared with the prior art method that relies on operators to collect and compare various information to determine the fault point, the fault method provided in this invention can achieve automatic fault location through various characteristic identifiers, thereby reducing the risk of human subjective judgment errors. Furthermore, this method can quickly determine the fault location, providing operators with the conditions to quickly isolate the fault and restore power supply to the non-faulty parts, minimizing the power outage time at non-faulty points and protecting the electrical load. Therefore, compared with the prior art, this invention can automatically determine the fault point in the branch structure of the distribution network, thereby quickly restoring power supply to non-faulty points and improving the reliability of the distribution network power supply.

[0076] Based on the above embodiments, optionally, the preset trip matrix includes: a trip matrix for the grounding transformer, specifically including: when the operating grounding transformer reports a branch structure with a ground fault, controlling the zero-sequence protection of the operating grounding transformer to operate within a time limit, causing the operating grounding transformer to issue a first action signal, thereby tripping the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located; if the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located trips, and the operating grounding transformer still reports a branch structure with a ground fault, then controlling the zero-sequence protection of the operating grounding transformer to operate within a second time limit, causing the operating grounding transformer to issue a second action signal, thereby tripping the low-voltage branch switch in the branch structure where the operating grounding transformer is located. The operating time of the second time limit of the zero-sequence protection is not earlier than the operating time of the first time limit of the zero-sequence protection.

[0077] In existing technologies, the trip matrix configuration for line grounding faults / busbar grounding faults in the secondary equipment of grounding transformers often does not distinguish the busbar where the fault point is located, tripping both low-voltage branch switches of the transformer simultaneously. This results in the non-selective disconnection of both busbars, causing simultaneous loss of voltage on both busbars. This may simultaneously disconnect electrical equipment in non-faulty branches, expanding the power outage area of ​​the grounding fault and causing unnecessary load loss on the non-faulty branch busbars on the low-voltage side of the transformer, affecting the reliability of power supply to users.

[0078] In the tripping matrix of the grounding transformer provided in the embodiments of the present invention, with Figure 1 Taking the operation of the first grounding transformer 507 as an example, when the secondary equipment of the first grounding transformer 507 reports a grounding fault, the zero-sequence protection time-limited function of the first grounding transformer 507 (specifically, the 'high-voltage side zero-sequence protection time-limited function') trips, opening the second transformer low-voltage branch switch 506. At this time, if the fault point is located in the second branch structure 12, for example, on the second busbar L2 or its lead-out lines, the second busbar L2 loses voltage due to the tripping of the second transformer low-voltage branch switch 506, and the fault point is isolated. In this case, the zero-sequence protection time-limited function of the first grounding transformer 507 (specifically, the 'high-voltage side zero-sequence protection time-limited function') does not operate, and the first busbar L1 operates normally. If the fault point is located in the first branch structure 11, for example, on the first busbar L1 or its lead-out lines, the secondary equipment of the first grounding transformer 507 still reports a grounding fault, and the zero-sequence protection time-limited function of the first grounding transformer 507 trips, opening the first transformer low-voltage branch switch 502, causing the first busbar L1 to lose voltage, thereby isolating the fault point. Correspondingly, when the second grounding transformer 508 is in operation, if the second grounding transformer 508 detects a grounding fault, the zero-sequence protection of the second grounding transformer 508 will trip the first low-voltage branch switch 502 within a time limit, and the zero-sequence protection of the second low-voltage branch switch 506 will trip within a time limit.

[0079] In summary, based on the trip matrix configuration of the grounding transformer provided in this embodiment of the invention, regardless of which grounding transformer is operating on-site, there is a 50% probability that the non-faulty busbar will not lose voltage in the event of a grounding fault. Secondly, in the remaining 50% probability, when the non-faulty busbar loses voltage, the fault point can be quickly identified by the protection action signal, and power supply to the non-faulty busbar can be restored after isolating the fault.

[0080] Based on the above embodiments, optionally, the preset trip matrix further includes: a trip matrix for backup protection devices and a trip matrix for bay devices. The trip matrix for backup protection devices includes: when at least one backup protection device detects a phase-to-phase fault in its corresponding branch structure, controlling the overvoltage overcurrent time-delay action of the backup protection device in the branch structure where the phase-to-phase fault is located, causing the backup protection device to issue a third action signal, thereby causing the low-voltage branch switch in the branch structure where the phase-to-phase fault is located to trip.

[0081] The tripping matrix of the bay equipment includes: when at least one bay equipment responds to a fault in the line it is connected to, the control bay equipment responding to the fault issues a fourth action signal, thereby causing the bay switch of the line connected to the responding bay equipment to trip.

[0082] Figure 3 This is a flowchart illustrating a fault protection method for a transformer with a dual-branch connection provided in an embodiment of the present invention. Figure 3 The document mainly outlines the detailed steps of the fault location process, which are explained in detail below. See also... Figure 3 The fault location includes the following steps:

[0083] S211, Receive the main accident signal.

[0084] Among these, backup protection equipment, grounding transformers, and bay equipment can all issue a general fault signal after operation (e.g., after generating an operation signal). This step can involve receiving any one of the general fault signals.

[0085] S212. After a preset delay time, initialize each feature identifier.

[0086] The preset delay time can be set according to the protection time setting value of each protection device in the system. It is necessary to ensure that after receiving any total fault signal, the system waits until the total protection setting time of all protection devices in that round of protection has elapsed before starting the fault point screening to avoid missing action information. For example, initializing each feature identifier can be done by setting each feature identifier to 0. If each feature identifier is subsequently assigned a value, its value will change; if it is not assigned a value, the value of the feature identifier will remain unchanged at 0.

[0087] S213. Determine if there is an undervoltage busbar; if yes, proceed to S214; if no, proceed to S218.

[0088] This step can be determined based on historical electrical quantity data stored in the dispatch center's backend, or by directly reading the judgment results from other departments in the backend.

[0089] S214. Assign values ​​to the action identifiers of the backup protection equipment based on the action information of the backup protection equipment, and assign values ​​to the action identifiers of the grounding transformer based on the action information of the grounding transformer.

[0090] The assignment of action flag values ​​to backup protection devices based on their action information includes: if the backup protection device does not operate under overvoltage overcurrent for one time limit, the action flag value of the backup protection device is set to 0; if the backup protection device operates under overvoltage overcurrent for one time limit, the action flag value of the backup protection device is set to 1.

[0091] Assigning values ​​to the grounding transformer's operation flag based on its operation information can specifically include: If neither the zero-sequence protection time limit one nor the zero-sequence protection time limit two of the grounding transformer operates, then the grounding transformer's operation flag is set to 0. If only the zero-sequence protection time limit one of the grounding transformer operates, and the zero-sequence protection time limit two does not operate, then the grounding transformer's operation flag is set to 1, and the zero-sequence protection time limit one of the grounding transformer is recorded as the grounding transformer's operation time. If the zero-sequence protection time limit two of the grounding transformer operates, then the grounding transformer's operation flag is set to 1, and the zero-sequence protection time limit two of the grounding transformer is recorded as the grounding transformer's operation time.

[0092] S215. Determine whether the action indicators of all backup protection devices and all grounding transformers are 0; if yes, proceed to S216; if no, proceed to S217.

[0093] S216. The fault is located in the voltage transformer connected to the upstream power supply or the undervoltage bus of the branch structure.

[0094] If there is a busbar undervoltage, and the action indicators of all backup protection devices and all grounding transformers are 0, it means that the busbar-related protection devices have not operated but the busbar is undervoltage. In this case, it can be determined that the upstream power supply failure has caused the busbar power supply interruption, or the voltage transformer (PT) failure has made the voltage detection result unreliable, and the above judgment result will be output. In actual operation, the operators can investigate the above two reasons.

[0095] S217. Set the bus fault flag to 1 and set the relevant equipment action flag of the undervoltage bus to 1.

[0096] The bus fault indicator indicates whether there is an undervoltage bus on the low-voltage side of the transformer. When one bus is undervoltage, or both busbars are undervoltage, the bus fault indicator is set to 1. In other words, when there is a backup protection device and / or grounding transformer with an action indicator of 1, it indicates that a busbar has been disconnected, and therefore the bus fault indicator is set to 1.

[0097] When the relevant equipment action flag is 1, it indicates that the busbar is disconnected due to the correct operation of the protection equipment causing the corresponding low-voltage branch switch to trip. Specifically, when the backup protection equipment action flag is 1, the relevant equipment action flag of the busbar in the branch structure corresponding to the backup protection equipment is assigned 1; when the grounding transformer action flag is 1, and the grounding transformer action time is zero-sequence protection time limit 2, the relevant equipment action flag of the busbar connected to the grounding transformer is assigned 1; when the grounding transformer action flag is 1, and the grounding transformer action time is zero-sequence protection time limit 1, the relevant equipment action flag of the busbar not directly connected to the grounding transformer is assigned 1.

[0098] S218. Determine if the bus fault flag is 0; if yes, proceed to S219; if no, proceed to S220.

[0099] S219. Obtain the operation information of all bay devices and all bay switches in the two branch structures, and determine the health status of each bay device and each bay switch accordingly.

[0100] When the bus fault indicator is 0, it means there is no bus voltage loss. In this case, the health status analysis of the bay equipment and bay switches on the line reporting the overall fault signal should be performed first. Then, the health status analysis of other bay equipment and bay switches should be performed to avoid missing abnormal bays. Although the faulty line is disconnected after the bay switch operates in this case, preventing the downstream protection from overstepping its limit, it does not guarantee that the bay switch is free from abnormalities such as slow tripping. Therefore, it is essential to determine the health status of each bay equipment and bay switch based on their operation information. By searching and judging the relevant protection information of all bay equipment and bay switches on both busbars, it can be determined whether the protection of each bay operates normally or whether there are any abnormalities in the switches that warrant attention, thereby ensuring the safety and reliability of subsequent protection processes.

[0101] S220. Assign values ​​to the fault identifiers of each bay switch based on the operation information of each bay device and the operation information of each bay switch in the branch structure where the undervoltage busbar is located; wherein, when the fault identifier of any bay switch is 1, the bay fault over-level identifier is assigned 1.

[0102] Specifically, assigning a fault identifier to the bay switch based on the action information of the bay equipment and the action information of the bay switch may include: if the bay equipment issues a fourth action signal and the corresponding bay switch action information includes occupancy information and protection action return information, then the fault identifier of the bay switch is assigned 0; if the bay equipment issues a fourth action signal, but the corresponding bay equipment action information does not include occupancy information and / or protection action return information, then the fault identifier of the bay switch is assigned 1.

[0103] For example, there are several types of fault indications for interval switches. Some of them are described below:

[0104] In one implementation, optionally, the fault identifier is a failure to operate identifier. When the interval device issues a fourth action signal, but the corresponding interval switch action information does not include the position information, the failure to operate identifier of the interval switch is assigned 1.

[0105] In another implementation, optionally, the fault identifier is a slow-opening identifier. When the bay equipment issues a fourth action signal, the bay switch's action information includes opening information, but if the bay switch's opening time exceeds a preset time threshold, the slow-opening identifier of the bay switch is assigned 1. The preset time threshold can be set based on the zero-sequence protection two-time-limit action time of the grounding transformer or the overcurrent protection one-time-limit action time of the low-voltage branch switch, or it can be set based on other on-site factors.

[0106] In another embodiment, optionally, the fault identifier is an unisolated fault identifier. When the bay device issues a fourth action signal, the bay switch action information includes squaring information, the bay switch squaring time is less than a preset time threshold, but the bay switch action information does not include protection action return information, the unisolated fault identifier of the bay switch is assigned 1.

[0107] Specifically, the process of obtaining the interval time of the interval switch may include:

[0108] The search queries the reporting time of the action signal of the bay device within a first preset time period (e.g., the time when the fourth action signal is issued), and records the first action signal reporting time of the bay device within the first preset time period as the action time of the bay device; wherein, the first preset time period includes the time when the total fault signal is reported. The first preset time period can be a time period in the middle of the total fault signal. The first preset time period is set based on the consideration of not omitting key action information; specifically, when a line fault occurs, the bay device on the line will first issue the (fourth) action signal and report the total fault signal. If the bay switch corresponding to the bay device fails, causing subsequent bus-related protection devices to overstep their limits, then the actual bus voltage loss occurs after the total fault signal is reported; however, when a bus fault occurs, the bus voltage loss time is the time when the bus-related protection devices control the lowering branch switch to trip, and the fault occurs before the switch trips. Therefore, considering all factors, a time period of 5 seconds before and after the total fault signal reporting time (total fault time) can be selected as the first preset time period.

[0109] If there is reclosing information of the bay switch within the first preset time period, the last action signal reporting time of the bay device within the first preset time period will be recorded as the reclosing action time of the bay device (equivalent to the reporting time of the action signal when the bay device issues an action signal again after the bay switch is reclosed to control the bay switch in operation to trip again).

[0110] The search process retrieves the reporting time of the interval switch's position signal within a second preset time period. If no position signal reporting time is obtained within the second preset time period, it can be determined that the interval switch's operation information lacks position information. If at least one position signal reporting time is found within the second preset time period, the time difference between the first position signal reporting time and the start time of the second preset time period is recorded as the interval switch's position time. The start time of the second preset time period is either the operation time or the operation time after reclosing. For example, the second preset time period could be 3 seconds. Due to the quality issues of the interval switch itself, multiple position signals may be obtained within 3 seconds after receiving the operation signal (or the operation signal after reclosing), meaning there are multiple position signal reporting times. Therefore, to collect complete information about the interval switch, a search process within the second preset time period is set up here.

[0111] S221. Determine if the interval fault cascading flag is 1; if yes, proceed to S223; if no, proceed to S222.

[0112] In cases where a busbar undervoltage exists, a fault in any compartment switch can cause the related protection equipment on the busbar to malfunction. Therefore, in this situation, if the fault flag of any compartment switch is 1, the compartment fault malfunction flag will also be set to 1. Thus, when the busbar fault flag is 1 and the compartment fault malfunction flag is 0 (meaning the related equipment on the undervoltage busbar has a malfunction flag of 1, and all compartment switches in the branch structure where the undervoltage busbar is located have fault flags of 0), the fault can be determined to be located on the undervoltage busbar. Conversely, when the busbar fault flag is 1 and the compartment fault malfunction flag is 1 (meaning at least one compartment switch in the branch structure where the undervoltage busbar is located has a fault flag of 1), the fault can be determined to be located on the line containing the compartment switch with fault flag 1. The fault type of the compartment switch can be referenced from its fault flag type.

[0113] S222, Bus fault with related equipment action flag 1.

[0114] S223. Determine the fault location based on the fault indicator of each bay switch, and determine the fault type of the bay switch based on the type of fault indicator.

[0115] This embodiment uses S211-S223 to determine the fault location after a system failure.

[0116] The following is combined with Figures 4-8 The specific logic for determining the fault location is explained through a specific embodiment.

[0117] First, define the following feature identifier:

[0118] 1. i is the interval device number, i=1,2,......,N. N is the number of lines connected to a busbar, N is an integer greater than or equal to 2.

[0119] 2. M is the busbar number. M=1 marks the first busbar, and M=2 marks the second busbar.

[0120] 3. x1 is the relevant equipment action identifier for the first busbar. Relevant equipment refers to the equipment that controls the low-voltage branch switch to disconnect the busbar after the protection is activated. In this embodiment, the relevant equipment action identifier for the first busbar can be used to mark whether the grounding transformer and / or low-voltage backup protection that control the tripping of the first low-voltage branch switch are activated. 1 indicates that equipment is activated, and 0 indicates that none of them are activated.

[0121] 4. x2 is the relevant equipment operation indicator for the second busbar. As above, the relevant equipment operation indicator for the second busbar can be used to mark whether the grounding transformer and / or the low-voltage backup protection that control the tripping of the second low-voltage branch switch has been activated. 1 indicates that the equipment has been activated, and 0 indicates that none of them have been activated.

[0122] 5. Tmikk is the time stamp of the total fault signal reported by the i-th interval on the m-th bus.

[0123] 6. x is the bus fault identifier, where 1 indicates at least one bus fault and 0 indicates no bus fault.

[0124] 7. flag11 is the busbar undervoltage indicator for the first busbar, where 1 indicates undervoltage and 0 indicates no undervoltage.

[0125] 8. flag12 is the busbar undervoltage indicator for the second busbar, 1 for undervoltage and 0 for no undervoltage.

[0126] 9. flag2 is the interval fault over-level indicator. 1 indicates that the busbar voltage is lost due to the fault of the interval switch, and 0 indicates that there is no fault in the interval switch.

[0127] 10. flagJDB1 is the action indicator of the first grounding transformer, 1 for action and 0 for no action; flagJDB2 is the action indicator of the second grounding transformer, 1 for action and 0 for no action; Tjdb is the action time of the grounding transformer.

[0128] 11. flagZB1 is the action identifier of the first backup protection device, 1 means action, 0 means no action; flagZB2 is the action identifier of the second backup protection device, 1 means action, 0 means no action; Tzb is the action time of the backup protection device.

[0129] 12. flagMi3 is the failure indicator of the i-th bay switch on the M-th bus; 1 indicates that the switch has failed to operate, and 0 indicates that there is no failure to operate.

[0130] 13. flagMi4 is the slow-opening indicator for the i-th interval switch on the M-th bus. 1 indicates slow opening of the switch, and 0 indicates no slow-opening fault.

[0131] 14. flagMi5 is the unisolated fault identifier of the i-th bay switch on the M-th bus. 1 indicates an unisolated fault, and 0 indicates an isolated fault.

[0132] 15. TMiD1 is the operating time of the i-th bay device on the M-th bus, and TMiD2 is the operating time of the i-th bay device on the M-th bus after reclosing (the acceleration operating time after protection reclosing).

[0133] 16. Tch is the actual reclosing operation time of the bay switch.

[0134] 17. TMiF1 is the time to vacate after the protection operation of the i-th compartment switch on the M-th busbar, and TMiF2 is the time to vacate after the protection reclosing and acceleration operation of the i-th compartment switch on the M-th busbar; if there is no vacating time, then TMiFk (k=1,2) can be marked as 0s.

[0135] 18. Tst is the reference time used to determine the slow opening of each interval switch.

[0136] See Figures 4-8 The fault location determination process can be executed by the controller in the scheduling backend, including the following steps:

[0137] See Figure 4 When the dispatch backend receives a total fault signal from any bay device (e.g., the total fault signal from the i-th bay device on the m-th bus, time-stamped as Tmikk), it starts the program after a 10-second delay and initializes all flags. Specifically, flag11=0, flag12=0, flagJDB1=0, flagJDB2=0, flagZB1=0, flagZB2=0, flag2=0, x=0, x1=0, x2=0, M is the bus number m of the bay device that reported the total fault signal, and i is the bay number i of the bay device that reported the total fault signal.

[0138] Then, it determines whether each of the two busbars is undervoltage and proceeds to the branch process. The specific determination process includes: for the first busbar, determining whether its three-phase voltages Ua2, Ub2, and Uc2 are all less than 30% of the rated voltage Un; if so, setting the busbar undervoltage flag flag11 to 1; otherwise, flag11 remains 0. Similarly, for the second busbar, determining whether its three-phase voltages Ua6, Ub6, and Uc6 are all less than 30% of the rated voltage Un; if so, setting the busbar undervoltage flag12 to 1; otherwise, flag11 remains 0. After flag11 and flag12 are set, the process proceeds to the determination step S31.

[0139] Figure 5 The diagram illustrates the assignment process for the characteristic identifiers related to each grounding transformer and each backup protection device. See also... Figure 5 The process includes:

[0140] First, in S31, it is determined whether flag11 and flag12 are both 1, that is, whether both busbars are undervoltage. If so, the possible reason is that the zero-sequence protection of a grounding transformer has operated for two time limits, or that the overvoltage and overcurrent protection devices of both backup protection devices have operated for one time limit. Therefore, when flag11 and flag12 are both 1, the operation status judgment and characteristic identification assignment process of the relevant protection devices of each busbar is entered. If not, the judgment process of whether flag11 and flag12 are both 0 is entered in S32.

[0141] Specifically, when both flag11 and flag12 are 1, for the grounding transformer, firstly, it is determined whether the grounding transformer's switch is closed, i.e., whether the grounding transformer is in operation. If so, it is further determined whether the zero-sequence protection two-time delay of the grounding transformer has been activated. If the zero-sequence protection two-time delay of the grounding transformer has been activated, the activation flag of the grounding transformer is set to 1, and the activation time Tjdb of the grounding transformer is recorded as the activation time of the zero-sequence protection two-time delay of the grounding transformer. If the grounding transformer is not in operation or its zero-sequence protection two-time delay has not been activated, the activation flag of the grounding transformer remains 0. When the zero-sequence protection two-time delay of the first grounding transformer is activated, flagJDB1=1, Tjdb=Tjfb1(GLL2); when the zero-sequence protection two-time delay of the second grounding transformer is activated, flagJDB2=1, Tjdb=Tjfb2(GLL2). For backup protection devices, first determine if the backup protection device has activated; if so, continue to determine if the overcurrent protection device has activated its overvoltage protection time limit; if the overcurrent protection time limit has activated, then the activation flag of the backup protection device is set to 1, and the activation time Tzb is recorded as the overcurrent protection time limit activation time. If the backup protection device of the main transformer low-voltage branch does not activate or its overcurrent protection time limit has not activated, the activation flag of the backup protection device remains at 0. When the overcurrent protection time limit of the first backup protection device activates, flagZB1=1, Tzb=Tzb1(GL1); when the overcurrent protection time limit of the second backup protection device activates, flagZB2=1, Tzb=Tzb2(GL1).

[0142] In S32, it is determined whether both flag11 and flag12 are 0, that is, whether there is no busbar undervoltage. If yes, proceed to the judgment process in S34. If no, it indicates that there is a single busbar undervoltage in the system. The possible causes are the zero-sequence protection of a grounding transformer operating for a certain time, or the overcurrent protection of a certain backup protection device operating for a certain time. Therefore, if either flag11 or flag12 is 1, proceed to the operation status judgment and feature identifier assignment process of each busbar-related protection device.

[0143] Specifically, when either flag11 or flag12 is 1, first determine if flag11 = 1. If so, it indicates that the first busbar is undervoltage. At this point, if the cause of the first busbar undervoltage is the zero-sequence protection time-delay operation of the second grounding transformer, then flagJDB2 = 1, and Tjdb = Tjfb2(GL1); if the cause of the first busbar undervoltage is the overcurrent protection time-delay operation of the first backup protection device, then flagZB1 = 1, and Tzb = Tzb1(GL1). If flag11 ≠ 1, it indicates that flag12 = 1, meaning the second busbar is undervoltage. At this time, if the cause of the second busbar undervoltage is the zero-sequence protection of the first grounding transformer operating for a time limit, then flagJDB1=1, and Tjdb=Tjfb1(GL1); if the cause of the second busbar undervoltage is the overcurrent protection of the second backup protection device operating for a time limit, then flagZB2=1, and Tzb=Tzb2(GL1).

[0144] After the characteristic identifiers of each backup protection device and grounding transformer are assigned values, the judgment process of S33 is initiated.

[0145] Figure 6 The diagram illustrates the assignment process for the relevant equipment operation indicators of each busbar and the fault indicators of each bay device. See also... Figure 6 The process includes:

[0146] First, starting from S33, based on the operation flags and operation times of the busbar-related protection devices, it is determined which busbar-related protection device was used to trip, and values ​​are assigned to the busbar fault flag x and the busbar protection flags of each busbar accordingly. Specifically, when any one of flagJDB1=1 and Tjdb=Tjdb1(GLL2), flagJDB2=1 and Tjdb=Tjdb2(GL1), and flagZB1=1 is satisfied, it indicates that the busbar-related protection device used to trip the first busbar has been used. In this case, x=1, x1=1, and M is assigned the value 1. When any one of flagJDB2=1 and Tjdb=Tjdb2(GLL2), flagJDB1=1 and Tjdb=Tjdb1(GL1), and flagZB2=1 is satisfied, it indicates that the busbar-related protection device used to trip the second busbar has been used. In this case, x=1, x2=1, and M is assigned the value 2. If none of the above conditions are met, it is determined that the upstream power supply has disappeared or the PT has failed, causing the bus to lose voltage. In S32, if it is determined that flag11 and flag12 are both 0, x, x1 and x2 are all kept at 0, and M is kept at the m assigned in the initialization step.

[0147] After the values ​​of x, x1, x2, and M are assigned, the process of assigning fault indicators to each bay switch begins. Specifically, in S34, it is first determined whether x is 0. If it is, it indicates that there is no voltage loss on either bus. In this case, i and M remain at the values ​​assigned in the initialization step, and the process can directly proceed to S35 to assign fault indicators to the bay switches connected to the i-th line on the M-th bus, thus determining the health status of the bay switch. If not, it indicates that there is a voltage loss on the bus (the M-th bus is voltage loss as obtained in the relevant equipment action indicator assignment process). In this case, based on the value of M, step S35 can be executed only for all bay switches on the M-th bus to assign fault indicators, in order to determine whether the fault is on the line and to determine the specific location of the faulty line.

[0148] For detailed steps on assigning values ​​to the fault indicators of the S35 intermediate bay switch, please refer to [link / reference needed]. Figure 7 First, set the failure to operate flagMi3, slow opening flagMi4, ​​and unisolated fault flagMi5 of the i-th interval switch on the M-th busbar to 0 (equivalent to initializing various fault flags).

[0149] Then, the reporting times TMiDZj of each action signal of the bay device obtained within the first preset time period, including the reporting time Tkk of the total fault signal (i.e., the time represented by the timestamp Tmikk obtained before the fault location process delay start), are searched to obtain the protection action time of the bay device. The time range of the first preset time period can be adjusted according to the actual situation, for example, set to a period of 5 seconds before and after the reporting time Tkk of the total fault signal. Specifically, this step is as follows: the first time point TM1 within this time range is taken as the action time TMiD1 of the i-th bay device on the M-th bus. If the i-th bay switch on the M-th bus has a reclosing operation (i.e., the actual reclosing action time Tch is obtained), the last time point within this time range is taken as the reclosing action time TMiD2 of the i-th bay device on the M-th bus.

[0150] After obtaining the operating time TMiD1 and / or the reclosing operating time TMiD2 of the i-th bay device on the M-th bus, the fault identifiers of the i-th bay switch on the M-th bus are assigned values ​​according to the occupancy status of the corresponding protection operation. Specifically, k=1 indicates the process of assigning values ​​to the fault identifiers of the bay switch based on the occupancy information after the operating time TMiD1, and k=2 indicates the process of assigning values ​​to the fault identifiers of the bay switch based on the occupancy information after the reclosing operating time TMiD2.

[0151] Specifically, before searching for the quantile signal reporting time, the quantile time TMiFk can be initially set to 0. If a quantile signal reporting time TMiFkr is subsequently acquired, the quantile time TMiFk will be updated to a non-zero value, which is the difference between the first quantile signal reporting time TMiFk1 and TMiDk acquired within the second preset time period starting from TMiDk. If no quantile signal reporting time TMiFkr is subsequently acquired, the quantile time TMiFk remains at 0s. The duration of the second preset time period can be adjusted according to actual conditions, for example, set to 3 seconds.

[0152] When the interval time TMiFk remains at 0s, the interval switch is determined to have failed to operate, and flag2=1 and flagMi3=1 are set. Otherwise, it is determined whether the interval time meets the requirements.

[0153] If the interval switching time TMiFk ≤ 60ms, the interval switching time of the switch is considered normal. Further determination is needed to determine whether the switch has tripped, i.e., whether the protection action of the switch has returned. Otherwise, it is confirmed that the switch has a slow opening problem. Further determination can be made to determine whether the slow opening of the switch has caused the busbar to lose voltage.

[0154] Specifically, when TMiFk ≤ 60ms, if a protection action return flag is received, it indicates that the protection of the bay device operated correctly and the bay switch operated normally. Then, the system proceeds to determine if k equals 2, i.e., whether all information collection for the bay switch after the corresponding bay device's action time and after the reclosing action time has been completed. If k = 2, then fault identification marking for the bay switch under various conditions has been completed. If k ≠ 2, then the fault identifications of the bay switch are assigned values ​​based on the grading information after TMiD2 at the reclosing action time. If the protection action does not return, then the bay switch did not isolate the fault after its action (e.g., vacuum bubble breakdown), and flagMi5 is marked as 1, while flag2 is also marked as 1.

[0155] When TMiFk > 60ms, if the backup protection device operates, the reference time Tst for slow switching is set to equal the operating time Tzb of the backup protection device; if the grounding transformer operates, the reference time Tst for slow switching is set to equal the operating time Tjdb of the grounding transformer. Otherwise, the reference time Tst for slow switching is set to a reference threshold time, which can be adjusted according to the actual situation on site, for example, 250ms. When TMiFk ≤ Tst, it will not cause over-level protection operation, and only flagMi4=1 is marked; when TMiFk ≥ Tst, it indicates that the opening time of the bay switch exceeds the minimum operating time of the main transformer backup protection and / or grounding transformer protection, resulting in over-level protection, and flagMi4=1 is marked, and flag2=1 is also marked.

[0156] Once the fault flags of the aforementioned interval switches have been assigned values ​​(i.e., all fault flag assignments for k=1 and k=2 have been completed), the condition is satisfied. Figure 6 When the condition i≥N‖x=0 is met, the fault location determination process starting from S36 is initiated. For example, when only the operation time TMiD1 of the bay equipment is obtained, only the fault flag of the bay switch under the condition of k=1 is assigned; when the operation time TMiD2 after reclosing of the bay equipment is obtained, only the fault flag of the bay switch under the condition of k=2 is assigned.

[0157] Figure 8 The diagram illustrates the process of determining the fault location based on the values ​​of each characteristic identifier. See also... Figure 8 The process includes:

[0158] First, execute S36 to determine if x equals 1, i.e., to determine if there is a power failure bus. If there is no power failure bus, only determine if the bay equipment and bay switch on the i-th line of the M-th bus that reported the fault signal are abnormal. If flagMi4=1, output that the fault is located on the i-th line of the M-th bus, and the bay switch connected to the faulty line has been open for too long.

[0159] If there is a bus undervoltage, first check if flag2 is 1. If flag2 ≠ 1, it means that the bus undervoltage is not caused by the interval switch failure. Then proceed to the bus fault location criteria. If x1 = 1, the first bus is faulty. If x2 = 1, the second bus is faulty. If both x1 and x2 are 0, the upstream power supply is lost or the PT is faulty.

[0160] If flag2=1, the location of the faulty line and the fault type of the faulty switch are further determined based on the values ​​of flagMi3, flagMi4, ​​and flagMi5 of all switchboards on the undervoltage bus. Specifically, when flagMi3=1, the fault is located on the i-th line of the M-th bus, and the switchboard connected to the faulty line fails to operate; when flagMi4=1, the fault is located on the i-th line of the M-th bus, and the switchboard connected to the faulty line opens slowly; when flagMi5=1, the fault is located on the i-th line of the M-th bus, and the switchboard connected to the faulty line opens, but the fault is not actually isolated.

[0161] In summary, this invention provides a trip matrix configuration method that can reduce the possibility of power loss on non-faulty 10kV busbars. Furthermore, this invention combines limited protection action signals and switch change signals to determine whether the fault point is on the busbar. If the fault point is not on the busbar but within the 10kV line bay, the fault can be isolated as quickly as possible, and power supply to both busbars can be restored. If the fault point is on the busbar, it can distinguish which branch the faulty busbar is located on, in order to restore power supply to the fault-free 10kV busbar as quickly as possible, thereby effectively improving power supply reliability.

[0162] This invention also provides a fault protection device for a transformer with a dual-branch connection, which can execute the fault protection method for a transformer with a dual-branch connection provided in any embodiment of this invention, and has the corresponding functional modules and beneficial effects of the method. Figure 9 This is a structural schematic diagram of a fault protection device for a transformer with a dual-branch connection, provided in an embodiment of the present invention. See also... Figure 9 The fault protection device for the transformer with dual-branch connection includes: a protection action control module 310, an action identification assignment module 320, a fault identification assignment module 330, and a fault location module 340.

[0163] The protection action control module 310 is used to control the operation status of each bay device, each backup protection device, and the operating grounding transformer according to a preset trip matrix when a fault occurs in at least one branch structure. The action identifier assignment module 320 is used to assign action identifiers to the backup protection devices based on their action information, and to assign action identifiers to the grounding transformer based on its action information, when an undervoltage busbar exists. The fault identifier assignment module 330 is used to assign fault identifiers to each bay switch based on the action information of each bay device and each bay switch in the branch structure where the undervoltage busbar is located. The fault location module 340 is used to determine the fault location based on the action identifiers of the backup protection devices, the grounding transformer, and the bay switch, isolate the fault, and restore power supply to the non-faulty parts.

[0164] Based on the above embodiments, optionally, the preset trip matrix based on the protection action control module 310 specifically includes: when the operating grounding transformer reports the existence of a branch structure with a ground fault, controlling the zero-sequence protection of the operating grounding transformer to operate for a time limit, causing the operating grounding transformer to issue a first action signal, thereby causing the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located to trip; if the operating grounding transformer reports the existence of a branch structure with a ground fault after the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located trips, then controlling the zero-sequence protection of the operating grounding transformer to operate for a time limit, causing the operating grounding transformer to issue a second action signal, thereby causing the low-voltage branch switch in the branch structure where the operating grounding transformer is located to trip.

[0165] Optionally, based on the above embodiments, the preset trip matrix further includes: when at least one backup protection device reports a phase-to-phase fault in its corresponding branch structure, controlling the overvoltage overcurrent time-delay action of the backup protection device in the branch structure where the phase-to-phase fault occurs, causing the backup protection device to issue a third action signal, thereby causing the low-voltage branch switch in the branch structure where the phase-to-phase fault occurs to trip. When at least one bay device reports a fault in its line, controlling the bay device that reported the fault to issue a fourth action signal, thereby causing the bay switch of the line connected to the bay device that reported the fault to trip.

[0166] Based on the above embodiments, optionally, the action identifier assignment module 320 includes a first assignment unit and a second assignment unit. The first assignment unit is used to assign a value to the action identifier of the backup protection device according to the action information of the backup protection device; specifically, it is used to assign 0 to the action identifier of the backup protection device when the overcurrent protection device does not operate within the first time limit; and to assign 1 to the action identifier of the backup protection device when the overcurrent protection device operates within the first time limit. The second assignment unit is used to assign a value to the action identifier of the grounding transformer according to the action information of the grounding transformer; specifically, it is used to assign 0 to the action identifier of the grounding transformer when neither the first nor the second time limit of the zero-sequence protection of the grounding transformer operates; to assign 1 to the action identifier of the grounding transformer when the first time limit of the zero-sequence protection of the grounding transformer operates, but the second time limit of the zero-sequence protection of the grounding transformer does not operate, and to record the time of the first time limit of the zero-sequence protection of the grounding transformer as the action time of the grounding transformer; and to assign 1 to the action identifier of the grounding transformer when the second time limit of the zero-sequence protection of the grounding transformer operates, and to record the time of the second time limit of the zero-sequence protection of the grounding transformer as the action time of the grounding transformer.

[0167] Based on the above embodiments, optionally, the fault identification assignment module 330 is specifically used to assign 0 to the fault identification of the bay switch when the bay device issues a fourth action signal and the corresponding bay switch action information includes squaring information and protection action return information; and to assign 1 to the fault identification of the bay switch when the bay device issues a fourth action signal but the corresponding bay device action information does not include squaring information and / or protection action return information.

[0168] Based on the above embodiments, optionally, the fault location module 340 includes: a related equipment action identifier assignment unit and a location unit. The related equipment action identifier assignment unit is used to assign values ​​to the related equipment action identifiers according to the action identifiers of each backup protection device and each grounding transformer: specifically, when the action identifier of a backup protection device is 1, the related equipment action identifier of the bus in the branch structure corresponding to the backup protection device is assigned 1; when the action identifier of the grounding transformer is 1, and the grounding transformer operation time is zero-sequence protection time limit 2, the related equipment action identifier of the bus connected to the grounding transformer is assigned 1; when the action identifier of the grounding transformer is 1, and the grounding transformer operation time is zero-sequence protection time limit 1, the related equipment action identifier of the bus not directly connected to the grounding transformer is assigned 1. The positioning unit is used to determine the fault location based on the relevant equipment action indicators and the fault indicators of each bay switch. Specifically, when the relevant equipment action indicator of the undervoltage bus is 1 and the fault indicators of all bay switches in the branch structure where the undervoltage bus is located are 0, the fault is located on the undervoltage bus. When the relevant equipment action indicator of the undervoltage bus is 1 and the fault indicator of at least one bay switch in the branch structure where the undervoltage bus is located is 1, the fault is located on the line where the bay switch with fault indicator 1 is located.

[0169] Based on the above embodiments, optionally, the fault location module 340 is also used to determine that the fault is located in the voltage transformer connected to the upstream power supply of the branch structure or the voltage transformer connected to the undervoltage bus when there is an undervoltage bus and the operation indicators of all backup protection devices and all grounding transformers are 0.

[0170] Based on the above embodiments, optionally, there are multiple types of fault indicators for the interval switch, and the fault location module 340 can also determine the cause of the interval switch fault according to the type of fault indicator. For example, if the fault indicator is a failure to operate indicator, when the interval device sends a fourth action signal, but the corresponding interval switch's action information does not include squaring information, the failure to operate indicator of the interval switch is set to 1. Alternatively, if the fault indicator is a slow squaring indicator, when the interval device sends a fourth action signal, the interval switch's action information includes squaring information, but the squaring time of the interval switch is greater than a preset time threshold, the slow squaring indicator of the interval switch is set to 1. Alternatively, if the fault indicator is a non-isolated fault indicator, when the interval device sends a fourth action signal, the interval switch's action information includes squaring information, the squaring time of the interval switch is less than a preset time threshold, but the interval switch's action information does not include protection action return information, the non-isolated fault indicator of the interval switch is set to 1.

[0171] Based on the above embodiments, optionally, the bay device reports a total fault signal after operation. The process of the fault identification assignment module 330 obtaining the interval switch's occupancy time specifically includes: searching for the bay device's operation signal reporting time within a first preset time period, and recording the first operation signal reporting time of the bay device within the first preset time period as the bay device's operation time; wherein, the first preset time period includes the time when the total fault signal is reported. If there is reclosing information of the bay switch within the first preset time period, then the last operation signal reporting time of the bay device within the first preset time period is recorded as the reclosing operation time of the bay device. Searching for the bay switch's occupancy signal reporting time within a second preset time period. If at least one occupancy signal reporting time is found, then the time difference between the first occupancy signal reporting time within the second preset time period and the start time of the second preset time period is recorded as the bay switch's occupancy time; wherein, the start time of the second preset time period is the operation time or the reclosing operation time.

[0172] Based on the above embodiments, optionally, the fault protection device under the transformer dual-branch connection method further includes a health status determination module, which is used to obtain the operation information of all bay equipment and all bay switches in the two branch structures when there is no undervoltage bus after controlling the operation status of each bay equipment, each backup protection equipment and the operating grounding transformer according to the preset trip matrix, and to determine the health status of each bay equipment and each bay switch based on the operation information of each bay equipment and each bay switch.

[0173] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0174] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A fault protection method for a transformer with a dual-branch connection, characterized in that, The transformer has two branch structures connected to its low-voltage side. Each branch structure includes a busbar, a low-voltage branch switch, a grounding transformer, and a bay device. The low-voltage branch switch is connected between the low-voltage side of the transformer and the busbar. The grounding transformer is connected to the busbar. At least one line extends from the busbar, and each line is connected to a bay device in a one-to-one correspondence. The line is connected to the busbar via a bay switch, and the bay device controls the bay switch to trip. The transformer includes two backup protection devices, each corresponding to one of the two branch structures. These backup protection devices control the low-voltage branch switch to trip. During the operation of the two branch structures, one grounding transformer is in operation, and the other is in hot standby mode. The fault protection method for the transformer with dual-branch connection includes: When a fault occurs in at least one of the branch structures, the operating status of each of the interval devices, each of the backup protection devices and the operating grounding transformer is controlled according to a preset tripping matrix. If there is an undervoltage busbar, the action identifier of the backup protection device is assigned a value according to the action information of the backup protection device, and the action identifier of the grounding transformer is assigned a value according to the action information of the grounding transformer. The fault identifier of each of the interval switches is assigned a value based on the operation information of each of the interval devices and the operation information of each of the interval switches in the branch structure where the undervoltage busbar is located; The fault location is determined based on the operation indicators of the backup protection equipment, the operation indicators of the grounding transformer, and the fault indicators of the interval switch; the fault is isolated and the power supply to the non-faulty parts is restored. The preset trip matrix includes: When the operating grounding transformer detects a branch structure with a grounding fault, the zero-sequence protection of the operating grounding transformer is controlled to operate for a time limit, causing the operating grounding transformer to issue a first action signal, thereby causing the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located to trip. If the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located trips, and the branch structure where the operating grounding transformer has detected a grounding fault still exists, then the zero-sequence protection of the operating grounding transformer is controlled to operate under time-limited conditions, causing the operating grounding transformer to issue a second action signal, thereby causing the low-voltage branch switch in the branch structure where the operating grounding transformer is located to trip. When at least one of the backup protection devices reacts to a phase-to-phase fault in its corresponding branch structure, the backup protection device of the branch structure where the phase-to-phase fault is located is controlled to perform a time-limited overvoltage overcurrent operation, causing the backup protection device to issue a third action signal, thereby causing the low-voltage branch switch of the branch structure where the phase-to-phase fault is located to trip. When at least one of the interval devices reports a fault in the line it is connected to, the interval device that reports the fault issues sends a fourth action signal, thereby causing the interval switch of the line connected to the faulty interval device to trip.

2. The fault protection method for a transformer with a dual-branch connection as described in claim 1, characterized in that, Assigning values ​​to the action identifier of the backup protection device based on the action information of the backup protection device includes: if the backup protection device does not activate during the overvoltage overcurrent time limit, then the action identifier of the backup protection device is assigned 0; if the backup protection device activates during the overvoltage overcurrent time limit, then the action identifier of the backup protection device is assigned 1. The operation flag of the grounding transformer is assigned a value based on the operation information of the grounding transformer, including: if neither the zero-sequence protection time limit one nor the zero-sequence protection time limit two of the grounding transformer operates, the operation flag of the grounding transformer is set to 0; if the zero-sequence protection time limit one of the grounding transformer operates, but the zero-sequence protection time limit two of the grounding transformer does not operate, the operation flag of the grounding transformer is set to 1, and the time of the zero-sequence protection time limit one of the grounding transformer is recorded as the operation time of the grounding transformer; if the zero-sequence protection time limit two of the grounding transformer operates, the operation flag of the grounding transformer is set to 1, and the time of the zero-sequence protection time limit two of the grounding transformer is recorded as the operation time of the grounding transformer. Assigning a fault identifier to the interval switch based on the operation information of the interval device and the operation information of the interval switch includes: if the interval device issues a fourth operation signal and the corresponding interval switch operation information includes position information and protection operation return information, then the fault identifier of the interval switch is assigned 0; if the interval device issues a fourth operation signal, but the corresponding interval device operation information does not include position information and / or protection operation return information, then the fault identifier of the interval switch is assigned 1.

3. The fault protection method for a transformer with a dual-branch connection as described in claim 2, characterized in that, Determining the fault location based on the operation indicators of the backup protection equipment, the operation indicator of the grounding transformer, and the fault indicator of the interval switch includes: When the action flag of the backup protection device is 1, the relevant equipment action flag of the bus in the branch structure corresponding to the backup protection device is assigned 1; When the operation flag of the grounding transformer is 1 and the operation time of the grounding transformer is zero-sequence protection time limit, the operation flag of the relevant equipment on the bus connected to the grounding transformer is set to 1; When the operation flag of the grounding transformer is 1 and the operation time of the grounding transformer is the zero-sequence protection time limit, the operation flag of the relevant equipment on the bus that is not directly connected to the grounding transformer will be set to 1. When the relevant equipment action flag of the undervoltage bus is 1, and the fault flags of all bay switches in the branch structure where the undervoltage bus is located are 0, the fault is located on the undervoltage bus. When the relevant equipment operation flag of the undervoltage busbar is 1, and the fault flag of at least one compartment switch in the branch structure where the undervoltage busbar is located is 1, then the fault is located on the line where the compartment switch with fault flag 1 is located.

4. The fault protection method for a transformer with a dual-branch connection as described in claim 3, characterized in that, Determining the fault location based on the operation indicators of the backup protection equipment, the operation indicators of the grounding transformer, and the fault indicators of the bay switch also includes: If there is an undervoltage bus, and the operation indicators of all backup protection devices and all grounding transformers are 0, then the fault is located in the upstream power supply of the branch structure or the voltage transformer connected to the undervoltage bus.

5. The fault protection method for a transformer with a dual-branch connection as described in claim 2, characterized in that, The fault identifier is a failure to operate identifier. When the interval device issues a fourth action signal, but the corresponding interval switch action information does not include the position information, the failure to operate identifier of the interval switch is set to 1. Alternatively, the fault identifier is a slow separation identifier. When the interval device issues a fourth action signal, the action information of the interval switch includes separation information, but the separation time of the interval switch is greater than a preset time threshold, the slow separation identifier of the interval switch is assigned 1. Alternatively, the fault identifier is an unisolated fault identifier. When the interval device issues a fourth action signal, the action information of the interval switch includes squaring information, the squaring time of the interval switch is less than the preset time threshold, but the action information of the interval switch does not include protection action return information, the unisolated fault identifier of the interval switch is assigned 1.

6. The fault protection method for a transformer with a dual-branch connection as described in claim 5, characterized in that, The interval device reports the overall accident signal after it is activated; The process of obtaining the interval time of the interval switch includes: Search for the time when the action signal of the interval device is reported within the first preset time period, and record the first time when the action signal of the interval device is reported within the first preset time period as the action time of the interval device; wherein, the first preset time period includes the time when the total accident signal is reported; If there is reclosing information of the interval switch within the first preset time period, then the last action signal reporting time of the interval device within the first preset time period is recorded as the reclosing action time of the interval device. Search for the reporting time of the interval switch's position signal within the second preset time period; If at least one segment signal reporting time is found, the time difference between the first segment signal reporting time within the second preset time period and the start time of the second preset time period is recorded as the segment time of the interval switch; wherein, the start time of the second preset time period is the action time or the action time after overlap.

7. The fault protection method for a transformer with a dual-branch connection as described in claim 1, characterized in that, After controlling the operating status of each of the aforementioned bay devices, each of the aforementioned backup protection devices, and the operating grounding transformer according to the preset tripping matrix, the method further includes: If there is no undervoltage bus, the operation information of all bay devices and all bay switches in the two branch structures is obtained, and the health status of each bay device and each bay switch is determined based on the operation information of each bay device and each bay switch.

8. A fault protection device for a transformer with a dual-branch connection, characterized in that, The transformer has two branch structures connected to its low-voltage side. Each branch structure includes a busbar, a low-voltage branch switch, a grounding transformer, and a bay device. The low-voltage branch switch is connected between the low-voltage side of the transformer and the busbar. The grounding transformer is connected to the busbar. At least one line extends from the busbar, and each line is connected to a bay device in a one-to-one correspondence. The line is connected to the busbar via a bay switch, and the bay device controls the bay switch to trip. The transformer includes two backup protection devices, each corresponding to one of the two branch structures. These backup protection devices control the low-voltage branch switch to trip. During the operation of the two branch structures, one grounding transformer is in operation, and the other is in hot standby mode. The fault protection device for the transformer with dual-branch connection includes: The protection action control module is used to control the operation status of each bay device, each backup protection device and the operating grounding transformer according to a preset trip matrix when a fault occurs in at least one of the branch structures. The action identifier assignment module is used to assign an action identifier value to the backup protection device according to the action information of the backup protection device when there is an undervoltage bus, and to assign an action identifier value to the grounding transformer according to the action information of the grounding transformer. The fault identification assignment module is used to assign fault identification values ​​to each of the bay switches based on the operation information of each of the bay devices and the operation information of each of the bay switches in the branch structure where the undervoltage bus is located. The fault location module is used to determine the fault location based on the operation identifier of the backup protection device, the operation identifier of the grounding transformer, and the fault identifier of the interval switch, isolate the fault, and restore power supply to the non-faulty part. The preset trip matrix includes: When the operating grounding transformer detects a branch structure with a grounding fault, the zero-sequence protection of the operating grounding transformer is controlled to operate for a time limit, causing the operating grounding transformer to issue a first action signal, thereby causing the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located to trip. If the low-voltage branch switch in the branch structure where the hot standby grounding transformer is located trips, and the branch structure where the operating grounding transformer has detected a grounding fault still exists, then the zero-sequence protection of the operating grounding transformer is controlled to operate under time-limited conditions, causing the operating grounding transformer to issue a second action signal, thereby causing the low-voltage branch switch in the branch structure where the operating grounding transformer is located to trip. When at least one of the backup protection devices reacts to a phase-to-phase fault in its corresponding branch structure, the backup protection device of the branch structure where the phase-to-phase fault is located is controlled to perform a time-limited overvoltage overcurrent operation, causing the backup protection device to issue a third action signal, thereby causing the low-voltage branch switch of the branch structure where the phase-to-phase fault is located to trip. When at least one of the interval devices reports a fault in the line it is connected to, the interval device that reports the fault issues sends a fourth action signal, thereby causing the interval switch of the line connected to the faulty interval device to trip.

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