Relay protection system applied to 500kV double bus connection

Abstract

This invention provides a relay protection system for a 500kV double busbar configuration, comprising: a first line protection device for monitoring and controlling bay units at the 500kV voltage level; a first circuit breaker failure protection device for determining the protection action information of faulty equipment and the current information of circuit breakers that fail to operate; a first bus differential protection device for determining whether a busbar fault has occurred and disconnecting all circuit breakers on the busbar; a second line protection device for monitoring and controlling bay units at the 500kV voltage level; a second circuit breaker failure protection device for determining the protection action information of faulty equipment and the current information of circuit breakers that fail to operate; and a second bus differential protection device for determining whether a busbar fault has occurred and disconnecting all circuit breakers on the busbar.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology, specifically to a relay protection system applied to a 500kV double busbar connection configuration. Background Technology

[0002] In modern power systems, the correct operation of relay protection, reclosing, and circuit breakers is essential for the safe and stable operation of the power system. Different voltage levels have different effects and consequences on the winding saturation of current transformers, which in turn leads to different requirements and differences in the transient characteristics of current transformers imposed by protection devices at different voltage levels.

[0003] According to relevant standards and specifications, 500kV system bus differential protection generally uses TPY class current transformer secondary windings, while circuit breaker failure protection uses P class current transformer secondary windings. Therefore, when a 500kV AC power distribution device adopts a double busbar connection, failure protection cannot be achieved by the 500kV bus differential protection and needs to be configured independently. Based on the application experience of conventional projects, each 500kV circuit breaker is configured with a single set of circuit breaker failure protection, and each set of circuit breaker current transformers is configured with one set of P-class windings for connecting to the circuit breaker failure protection device.

[0004] In the existing technology, if the circuit breaker failure protection device is configured as a single unit, after a fault occurs, the circuit breaker in the corresponding bay needs to trip for operation and maintenance, which also means the loss of the corresponding power transmission capacity. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention provides a relay protection system applicable to a 500kV double busbar connection configuration, which can maintain the continuous and stable output of a 500kV double busbar connection power system.

[0006] The technical solution adopted in this invention is as follows:

[0007] A relay protection system for a 500kV double busbar configuration includes: a first line protection device for monitoring and controlling bay units at the 500kV voltage level; a first circuit breaker failure protection device connected to the first line protection device for determining the protection action information of faulty equipment and the current information of circuit breakers that fail to operate; a first bus differential protection device connected to the first circuit breaker failure protection device for determining whether a busbar fault has occurred and disconnecting all circuit breakers on the busbar; and a second line protection device. The line protection device is connected to the first circuit breaker failure protection device. The second line protection device is used to measure and control the bay unit at the 500kV voltage level. The second circuit breaker failure protection device is connected to the second line protection device and the first circuit breaker failure protection device. The second circuit breaker failure protection device is used to determine the protection action information of the faulty equipment and the current information of the circuit breaker that fails to operate. The second bus differential protection device is connected to the second circuit breaker failure protection device and the first circuit breaker failure protection device. The second bus differential protection device is used to determine whether a fault has occurred on the bus and to disconnect all circuit breakers on the bus.

[0008] In one embodiment of the present invention, the first line protection device, the first circuit breaker failure protection device and the first bus differential protection device are grouped with the second line protection device, the second circuit breaker failure protection device and the second bus differential protection device in different cabinets.

[0009] In one embodiment of the present invention, when a line fault occurs in the 500kV double busbar relay protection system, the line protection activates the external circuit breaker protection to fail. The circuit breaker protection is determined to be faulty. After the failure action, the failure contact is connected to the bus differential protection failure input of this bay. The bus differential protection then determines the failure current. At the same time, a short delay is set, and the bus differential protection failure action trips each bus bay.

[0010] In one embodiment of the present invention, when the converter transformer of the 500kV double busbar relay protection system fails, the three trip contacts of the converter transformer protection are respectively cross-connected to two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts is connected to the first circuit breaker failure protection device to start failure, and the second set of TJR contacts is connected to the second circuit breaker failure protection device to start failure. The circuit breaker protection determines failure. After failure operation, the failure contact is connected to the bus differential protection failure input of this bay. The bus differential protection internally determines the failure current again. At the same time, a short delay is set. The bus differential protection failure operation trips each bay of the bus.

[0011] In one embodiment of the present invention, the bus faults in the 500kV double busbar connection relay protection system include: line bay faults, converter transformer faults, bus tie bay faults, and sectional bay faults.

[0012] In one embodiment of the present invention, when a line bay of the 500kV double busbar connection relay protection system is faulted, the bus differential protection activates the external circuit breaker failure protection of the line bay. The circuit breaker protection is determined to be faulty, and after the failure action, it opens to trip the opposite side of the line protection.

[0013] In one embodiment of the present invention, when the converter transformer bay of the 500kV double busbar connection relay protection system fails, the three-trip contacts of the bus differential protection are connected to two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts is connected to the first circuit breaker failure protection device to start failure, and the second set of TJR contacts is connected to the second circuit breaker failure protection device to start failure.

[0014] In one embodiment of the present invention, when the bus tie interval of the 500kV double busbar connection relay protection system fails, the bus differential protection trips the bus tie and simultaneously activates the internal bus tie failure protection, thereby realizing the bus tie failure judgment internally.

[0015] In one embodiment of the present invention, when a sectional interval fault occurs in the 500kV double busbar connection relay protection system, the bus differential protection trips the sectional interval, activates the external circuit breaker protection failure protection of the sectional interval, and after the failure action, opens to the other bus differential protection.

[0016] In one embodiment of the present invention, when the bus coupler / section charging overcurrent of the 500kV double busbar connection relay protection system is activated, the bus coupler / section charging overcurrent protection activates the external bus coupler / section failure protection. The failure current is determined by the bus coupler / section protection, and the failure action contact opens the bus differential protection bus coupler / section interval failure input, which is then output after a time delay by the first bus differential protection device and the second bus differential protection device bus coupler / section interval failure logic.

[0017] The beneficial effects of this invention are:

[0018] This invention uses a first line protection device and a second line protection device to measure and control the 500kV voltage level bay unit, and uses two sets of circuit breaker failure protection devices to determine the protection action information of the faulty equipment and the current information of the activated circuit breaker, and uses two sets of bus differential protection devices to determine whether a bus fault has occurred and disconnect all circuit breakers on the bus. Thus, it can maintain the continuous and stable output of the 500kV double bus connection power system. Attached Figure Description

[0019] Figure 1This is a block diagram of a relay protection system applied to a 500kV double busbar connection configuration according to an embodiment of the present invention;

[0020] Figure 2 This is a double busbar wiring diagram of a 500kV AC system according to an embodiment of the present invention;

[0021] Figure 3 This is a timing logic diagram of a line fault failure coordination under one embodiment of the present invention;

[0022] Figure 4 This is a timing logic diagram of a converter transformer failure under a converter transformer fault, according to an embodiment of the present invention.

[0023] Figure 5 This is a remote transmission logic diagram of the starting line under a bus fault according to an embodiment of the present invention;

[0024] Figure 6 This is a timing logic diagram for line / converter transformer bay failure under a bus fault according to an embodiment of the present invention;

[0025] Figure 7 This is a timing logic diagram for bus tie-bar failure under a bus fault according to an embodiment of the present invention;

[0026] Figure 8 This is a timing logic diagram for sectional bay failure under bus fault according to an embodiment of the present invention;

[0027] Figure 9 This is a timing logic diagram of the failure coordination under the overcurrent operation of the bus charging in one embodiment of the present invention;

[0028] Figure 10 This is a timing logic diagram of failure coordination under segmented charging overcurrent operation according to an embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0030] Figure 1 This is a block diagram of a relay protection system applied to a 500kV double busbar connection configuration according to an embodiment of the present invention.

[0031] like Figure 1As shown, the relay protection system of this invention, applied to a 500kV double busbar connection configuration, includes: a first line protection device 10, a first circuit breaker failure protection device 20, a first bus differential protection device 30, a second line protection device 40, a second circuit breaker failure protection device 50, and a second bus differential protection device 60. The first line protection device 10 is used for measuring and controlling the bay unit at the 500kV voltage level; the first circuit breaker failure protection device 20 is connected to the first line protection device 10 and is used to determine the protection action information of the faulty equipment and the current information of the circuit breaker that fails to operate; the first bus differential protection device 30 is connected to the first circuit breaker failure protection device 20, and the first bus differential protection device 60... The first line protection device 30 is used to determine whether a fault has occurred on the busbar and to disconnect all circuit breakers on the busbar; the second line protection device 40 is connected to the first circuit breaker failure protection device, and the second line protection device is used to measure and control the bay unit at the 500kV voltage level; the second circuit breaker failure protection device 50 is connected to the second line protection device 40 and the first circuit breaker failure protection device 20, and the second circuit breaker failure protection device is used to determine the protection action information of the faulty equipment and the current information of the circuit breaker that fails to operate; the second bus differential protection device 60 is connected to the second circuit breaker failure protection device 50 and the first circuit breaker failure protection device 20, and the second bus differential protection device is used to determine whether a fault has occurred on the busbar and to disconnect all circuit breakers on the busbar.

[0032] Specifically, in a 500kV double-busbar power system, each circuit breaker current transformer of a single circuit breaker failure protection system is equipped with one P-class winding for connecting to the circuit breaker failure protection device. If the circuit breaker failure protection fails, the circuit breaker in the corresponding bay must trip. Therefore, this embodiment of the invention proposes a redundant configuration for circuit breaker failure protection, with two sets of failure protection devices simultaneously in operation. When one set of failure protection devices fails or malfunctions, the other set continues to perform the failure protection function, thereby maintaining the continuous and stable output of the 500kV double-busbar power system.

[0033] In one embodiment of the present invention, such as Figure 2 As shown, in a 500kV AC system with double busbar connection, the 1M / 2M double busbar connection access equipment may include two converter transformer incoming lines and two 500kV AC outgoing lines, and the 3M / 4M double busbar connection access equipment may include two converter transformer incoming lines and two 500kV AC outgoing lines. The entire 500kV double busbar connection power system forms 4 converter transformer incoming lines, 4 500kV AC outgoing lines, 2 sets of bus tie circuits, and 2 sets of sectional circuits.

[0034] In one embodiment of the present invention, the first line protection device 10, the first circuit breaker failure protection device 20, and the first bus differential protection device 30 can be grouped with the second line protection device 40, the second circuit breaker failure protection device 50, and the second bus differential protection device 60 in different cabinets. The power supply for the protection devices can be taken from different sections of the DC power supply panel.

[0035] In one embodiment of the present invention, the AC voltage circuit can be taken from different windings of the voltage transformer, and the AC current circuit can be connected in series from the same current transformer winding. If conditions permit, the AC current circuit can be selected from different windings of the current transformer, and the output contacts of the two sets of circuit breaker protection are connected in parallel to the operating box, the bus differential circuit, and the remote tripping circuit of the line protection. The circuit breaker position, low pressure blocking reclosing, and blocking reclosing contacts can be connected to the two sets of circuit breaker protection respectively.

[0036] Specifically, such as Figure 3 As shown, when a line fault occurs in a 500kV double-busbar relay protection system, the line protection activates an external circuit breaker protection failure. The circuit breaker protection determines a failure and, after its operation, the failure contact is connected to the bus differential protection's failure input for this bay. The bus differential protection then determines the failure current and, with a short delay, trips all busbar bays upon failure. The short delay can be 10ms, for example, to avoid AC / DC phase interference exceeding half a cycle.

[0037] Furthermore, such as Figure 4 As shown, when the converter transformer of the 500kV double busbar relay protection system fails, the three trip contacts of the converter transformer protection are cross-connected to the two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts is connected to the first circuit breaker failure protection device to start failure, and the second set of TJR contacts is connected to the second circuit breaker failure protection device to start failure. The circuit breaker protection is judged to be in failure. After the failure operation, the failure contact is connected to the bus differential protection in this bay failure input. The bus differential protection internally judges the failure current again. At the same time, a short delay is set. The bus differential protection failure operation trips each bay of the bus.

[0038] In one embodiment of the present invention, bus faults in a 500kV double-busbar relay protection system may include: line bay faults, converter transformer faults, bus tie bay faults, and sectional bay faults. For line bays and converter transformer bays, regardless of whether the bay protection or bus differential protection operates, the 500kV circuit breaker failure detection is achieved by external failure protection. The failure current setting and delay are both set in the external failure protection. The internal failure function of the corresponding bay of the 500kV bus differential protection is only used to trip all busbar switches when the external failure protection operates. For bus tie bays, failure can be achieved by internal logic when the bus differential protection operates. For sectional bays, failure can be achieved by external logic when the bus differential protection operates. When the external bus tie / sectional charging overcurrent protection operates, the failure current can first be determined by this protection, and after failure operation, it is output to the bus differential protection bus tie / sectional failure input. The internal failure current is determined and a delay is achieved. Among them, the failure judgment of the internal bus tie / segment interval in the bus differential protection can be realized by the TPY level winding, and the failure judgment in the external bus tie / segment charging overcurrent protection can be realized by the P level winding.

[0039] Specifically, such as Figure 5 and Figure 6 As shown, when a line bay of a 500kV double busbar relay protection system experiences a fault, the bus differential protection activates the external circuit breaker failure protection of the line bay. The circuit breaker protection determines that it has failed, and after the failure action, it sends a tripping signal to the opposite side of the line protection.

[0040] Furthermore, such as Figure 5 and Figure 6 As shown, when a fault occurs in the converter transformer bay of a 500kV double-busbar relay protection system, the three-trip contacts of the bus differential protection are connected to two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts initiates the failure of the first circuit breaker failure protection device, and the second set of TJR contacts initiates the failure of the second circuit breaker failure protection device. Specifically, the bus differential protection initiates the external circuit breaker failure protection of the converter transformer bay, and the circuit breaker protection determines failure. It should be noted that the bus differential protection will simultaneously initiate the internal transformer bay failure protection, determining the failure current. The failure delay is only a short delay; the internal failure will initiate before the external circuit breaker failure protection operates, or even within the time between the bus differential protection operation and the disconnection of the fault current.

[0041] Furthermore, such as Figure 7 As shown, when the bus tie interval of the 500kV double busbar relay protection system fails, the bus differential protection trips the bus tie and simultaneously activates the internal bus tie failure protection, which is internally used to determine the bus tie failure.

[0042] Furthermore, such as Figure 8As shown, when a sectional interval of a 500kV double busbar relay protection system fails, the bus differential protection trips the sectional interval, activates the external circuit breaker protection failure protection of the sectional interval, and after the failure operation, it opens to the other bus differential protection.

[0043] In one embodiment of the present invention, such as Figure 9 and Figure 10 As shown, when the bus coupler / section charging overcurrent of the 500kV double busbar connection relay protection system is activated, the bus coupler / section charging overcurrent protection will activate the external bus coupler / section failure protection. The failure current is determined by the bus coupler / section protection, and the failure action contact opens the bus differential protection bus coupler / section interval failure input. After the first bus differential protection device and the second bus differential protection device bus coupler / section interval failure logic delay output.

[0044] In summary, the relay protection system for a 500kV double busbar connection according to the embodiments of the present invention measures and controls the bay units at the 500kV voltage level through the first and second line protection devices, and determines the protection action information of the faulty equipment and the current information of the operating circuit breaker through two sets of circuit breaker failure protection devices, and determines whether a busbar fault has occurred and disconnects all circuit breakers on the busbar through two sets of bus differential protection devices. Thus, it can maintain the continuous and stable output of the 500kV double busbar connection power system.

[0045] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0048] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0050] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0051] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0052] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0053] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0054] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A relay protection system for a 500kV double busbar configuration, characterized in that, include: The first line protection device is used to measure and control the 500kV voltage level bay unit. The first circuit breaker failure protection device is connected to the first line protection device. The first circuit breaker failure protection device is used to determine the protection action information of the faulty equipment and the current information of the circuit breaker that fails to operate. The first bus differential protection device is connected to the first circuit breaker failure protection device. The first bus differential protection device is used to determine whether a fault has occurred on the bus and to disconnect all circuit breakers on the bus. The second line protection device is connected to the first circuit breaker failure protection device. The second line protection device is used to measure and control the 500kV voltage level bay unit. The second circuit breaker failure protection device is connected to the second line protection device and the first circuit breaker failure protection device. The second circuit breaker failure protection device is used to distinguish the protection action information of the faulty equipment and the current information of the circuit breaker that fails to operate. The second bus differential protection device is connected to the second circuit breaker failure protection device and the first circuit breaker failure protection device. The second bus differential protection device is used to determine whether a fault has occurred on the busbar and to disconnect all circuit breakers on the busbar. When a line fault occurs in the 500kV double busbar relay protection system, the line protection activates the external circuit breaker protection. The circuit breaker protection is deemed to have failed, and after its failure action, the failure contact is connected to the bus differential protection's failure input for this bay. The bus differential protection then determines the failure current and, with a short delay, trips all busbar bays upon failure. When the converter transformer of the 500kV double busbar relay protection system fails, the three trip contacts of the converter transformer protection are cross-connected to the two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts is connected to the first circuit breaker failure protection device to start failure, and the second set of TJR contacts is connected to the second circuit breaker failure protection device to start failure. The circuit breaker protection is judged to be in failure. After the failure action, the failure contact is connected to the bus differential protection failure input of this bay. The bus differential protection internally judges the failure current again. At the same time, a short delay is set. The bus differential protection failure action trips each bay of the busbar.

2. The relay protection system applied to a 500kV double busbar connection configuration according to claim 1, characterized in that, The first line protection device, the first circuit breaker failure protection device, and the first bus differential protection device are grouped with the second line protection device, the second circuit breaker failure protection device, and the second bus differential protection device in different cabinets.

3. The relay protection system applied to a 500kV double busbar connection configuration according to claim 1, characterized in that, Busbar faults in the 500kV double busbar relay protection system include: line bay faults, converter transformer faults, bus tie bay faults, and sectional bay faults.

4. The relay protection system applied to a 500kV double busbar connection configuration according to claim 3, characterized in that, When a line bay fault occurs in the 500kV double busbar relay protection system, the bus differential protection activates the external circuit breaker failure protection of the line bay. The circuit breaker protection determines that it has failed, and after the failure action, it sends a tripping signal to the opposite side of the line protection.

5. The relay protection system applied to a 500kV double busbar connection configuration according to claim 4, characterized in that, When the converter transformer bay of the 500kV double busbar relay protection system fails, the three-trip contacts of the bus differential protection are connected to the two sets of TJR circuits of the first circuit breaker failure protection device. The first set of TJR contacts is connected to the first circuit breaker failure protection device to start failure, and the second set of TJR contacts is connected to the second circuit breaker failure protection device to start failure.

6. The relay protection system applied to a 500kV double busbar connection configuration according to claim 5, characterized in that, When the bus coupler interval of the 500kV double busbar relay protection system fails, the bus differential protection trips the bus coupler and simultaneously activates the internal bus coupler failure protection, which is internally used to determine the bus coupler failure.

7. The relay protection system applied to a 500kV double busbar connection configuration according to claim 6, characterized in that, When a sectional interval fault occurs in the 500kV double busbar connection relay protection system, the bus differential protection trips the sectional interval, activates the external circuit breaker protection failure protection of the sectional interval, and after the failure action, opens to the other bus differential protection.

8. The relay protection system applied to a 500kV double busbar connection configuration according to claim 1, characterized in that, When the 500kV double busbar connection relay protection system operates with a bus coupler / section charging overcurrent, the bus coupler / section charging overcurrent protection activates the external bus coupler / section failure protection. The bus coupler / section protection determines the failure current, and the failure action contact opens the bus differential protection bus coupler / section interval failure input, which is then output after a time delay by the first bus differential protection device and the second bus differential protection device bus coupler / section interval failure logic.

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