Control Method and Device for Multi-Mode Operation of Standby Power Supply System of Nuclear Power Unit

Abstract

This application belongs to the technical field of operation control of the standby power supply system in nuclear power plants, and specifically relates to a control method and device for multi-mode operation of the standby power supply system of a nuclear power unit. The method includes: determining multiple operation modes of the standby power supply system; and selecting a corresponding operation mode from the multiple operation modes according to the operation conditions of the nuclear power unit under different conditions. The embodiments of this application provide a variety of operation mode combinations for the standby power supply of a nuclear power plant, making the operation mode of in-station equipment flexible, facilitating the production operation dispatching management of the power grid, and improving the reliability of the standby power supply system.

Description

Technical Field

[0001] This application belongs to the technical field of operation control of the standby power supply system in nuclear power plants, and particularly relates to a control method and device for multi-mode operation of the standby power supply system of nuclear power units. Background Art

[0002] The main functions of the standby power supply system in a nuclear power plant are as follows: when the unit is shut down and the 500 kV main power supply system is lost, it operates with the plant load; when the voltage level at the motor outlet terminal is sufficient, it self-starts the load of the unit to meet the capacity and duration requirements of the transient process; the in-plant standby power supply is configured with one standby transformer per unit, and one standby transformer can ensure the load requirements for the normal shutdown and outage of one unit, etc.

[0003] The standby power supply system of a certain nuclear power plant is designed with two 220 kV standby power supply lines taken from the local power grid. The in-station wiring mode is double busbars with a bus coupler, which supplies power to the startup transformers (also called auxiliary transformers) of Units 1-6, and the intervals for the expansion of Units 7-8 are reserved.

[0004] During the normal operation of the unit, the standby power supply system always maintains the feeder operation mode of single-sided power supply. During the major overhaul of a certain unit, due to the outage of the main transformer or the need of the power grid operation mode, a situation of double-sided power supply may occur, and in this case, the mode needs to be switched. Since it involves multiple operation modes, and the operation modes of the relay protection are different in different modes, if not adjusted in time, a protection dead zone will occur, resulting in the failure to cut off the fault in time, which poses a threat to the safe operation of the equipment. Summary of the Invention

[0005] The purpose of this application is to provide a control method and device for multi-mode operation of the standby power supply system of nuclear power units, to solve the problem in the prior art that if the operation mode is not adjusted in time, a protection dead zone will occur, the fault cannot be cut off in time, which poses a threat to the safe operation of the equipment. The various operation modes of the 220 kV standby power supply are studied, and the relay protection adjustment methods for the corresponding modes are formulated to realize the control of multi-mode operation of the standby power supply system of nuclear power units.

[0006] Technical solutions to achieve the purpose of this application:

[0007] An embodiment of this application provides a control method for multi-mode operation of the standby power supply system of nuclear power units, and the method includes:

[0008] Determine multiple operation modes of the standby power supply system;

[0009] According to the operating conditions of the nuclear power unit, select the corresponding operation mode from the multiple operation modes under different conditions.

[0010] Optionally, the multiple operation modes include:

[0011] 1 Mode: Unilateral power supply operation mode, with weak current response enabled for line protection;

[0012] 2 Mode: Bilateral power supply operation mode, with line protection set to trip and reclosing disabled;

[0013] 3 Mode: Short-term tie line power supply operation mode, with normal settings enabled, line protection set to trip, and reclosing enabled;

[0014] 4 Mode: Long-term tie line power supply operation mode, with loop closing settings enabled, line protection set to trip, backup protection enabled, and reclosing enabled.

[0015] Optionally, selecting the corresponding operation mode from the multiple operation modes according to the operating conditions of the nuclear power unit specifically includes:

[0016] During the grid connection operation of the nuclear power unit, the operation mode of the standby power supply system is Mode 1;

[0017] During the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, the operation mode is Mode 2;

[0018] When the power supply of standby power bus 1 is switched from line 1 to line 2, the operation mode is Mode 3;

[0019] When required by the power grid to operate with a long-term tie line, the operation mode is Mode 4.

[0020] Optionally, during the grid connection operation of the nuclear power unit, the operation mode of the standby power supply system being Mode 1 specifically includes:

[0021] During the grid connection operation of the nuclear power unit, the standby power supply system operates in Mode 1, with unilateral power supply, weak current response enabled for line protection. When a 220 kV line trip occurs, the circuit breaker on the opposite side trips, and the circuit breaker on the local side remains closed. If it is an instantaneous fault, the circuit breaker on the opposite side is immediately reclosed.

[0022] Optionally, during the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, the operation mode being Mode 2 specifically includes:

[0023] During the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, there will be two power sources: the 220 kV line and the diesel generator. In the case of bilateral power supply, it is necessary to switch from Mode 1 to Mode 2, set the line protection to trip, and disable the reclosing. At this time, if a fault occurs, the circuit breakers on both the opposite side and the local side will trip simultaneously to eliminate the protection dead zone.

[0024] Optionally, when the power supply of the standby power bus 1 is switched from line 1 to line 2, the operation mode is mode 3, which specifically includes:

[0025] When the standby power supply operates in mode 1 or mode 2, if it is necessary to switch the power supply of the standby power bus 1 from line 1 to line 2, the operation mode can be switched to mode 3; in this mode, the bus-tie breaker will be closed for a short time, and the reclosing protection will be enabled. If the closed-loop state is maintained after the closed-loop operation is completed, the operation mode will be adjusted to mode 4; if the local breaker of line 1 is opened after the closed-loop operation is completed, the mode will be changed back to mode 1 or mode 2.

[0026] Optionally, when operating with a tie line in accordance with the requirements of the power grid, the operation mode is mode 4, which specifically includes:

[0027] When operating with a tie line in accordance with the requirements of the power grid, the operation mode is mode 4. In this mode, the closed-loop setting value is enabled, the line protection is set to trip, the backup protection is enabled, and the reclosing is enabled; after this operating condition ends, it is changed back to mode 1.

[0028] The embodiment of the present application also provides a control device for multi-mode operation of a nuclear power unit standby power supply system. The device includes:

[0029] A mode determination module for determining multiple operation modes of the standby power supply system;

[0030] A mode switching module for selecting a corresponding operation mode from the multiple operation modes according to the operating conditions of the nuclear power unit.

[0031] The beneficial technical effects of the present application are as follows:

[0032] (1) The control method and device for multi-mode operation of a nuclear power unit standby power supply system provided by the embodiment of the present application provide multiple operation mode combinations for the standby power supply of a nuclear power plant, making the operation mode of in-station equipment flexible, facilitating the power grid production operation dispatching management, and improving the reliability of the standby power supply system;

[0033] (2) The control method and device for multi-mode operation of a nuclear power unit standby power supply system provided by the embodiment of the present application propose a relay protection adjustment scheme for different operating conditions, improve the reclosing success rate in case of a high-voltage line fault during single-sided power supply, effectively avoid the protection dead zone during double-sided power supply, prevent equipment damage, and enable operators to make accurate judgments, thereby improving the success rate of mode switching. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of a nuclear power unit standby power supply system in an embodiment of the present application;

[0035] Figure 2 Schematic flow chart of a control method for multi - mode operation of an emergency power supply system of a nuclear power unit provided by an embodiment of the present application;

[0036] Figure 3 Schematic structural diagram of a control device for multi - mode operation of an emergency power supply system of a nuclear power unit provided by an embodiment of the present application. Specific embodiments

[0037] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the following described embodiments are only a part of the embodiments of the present application, rather than all. Based on the embodiments described in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0038] For ease of understanding, Figure 1 A schematic structural diagram of an emergency power supply system of a nuclear power unit is shown. The following will describe a control method and device for multi - mode operation of an emergency power supply system of a nuclear power unit provided by an embodiment of the present application in conjunction with Figure 1 the structure shown.

[0039] See Figure 2 , which is a schematic flow chart of a control method for multi - mode operation of an emergency power supply system of a nuclear power unit provided by an embodiment of the present application.

[0040] A control method for multi - mode operation of an emergency power supply system of a nuclear power unit provided by an embodiment of the present application includes:

[0041] S101: Determine multiple operation modes of the emergency power supply system;

[0042] S102: According to the operating conditions of the nuclear power unit, select the corresponding operation mode from multiple operation modes under different conditions.

[0043] In an example, if the emergency power supply system operates in multiple modes, the multiple operation modes include:

[0044] Mode 1: Unilateral power supply operation mode, with weak - current response enabled for line protection;

[0045] Mode 2: Bilateral power supply operation mode, with line protection set to trip and reclosing disabled;

[0046] Mode 3: Short - term tie - line power supply operation mode, with normal settings enabled, line protection set to trip, and reclosing enabled;

[0047] 4 Mode: Long-term tie-line power supply operation mode, loop closing setting enabled, line protection switched to trip, backup protection enabled, reclosing enabled.

[0048] Then, in some possible implementation manners of the embodiments of the present application, step S102 may specifically include:

[0049] During the grid connection operation of the nuclear power unit, the operation mode of the standby power supply system is Mode 1;

[0050] During the major overhaul or minor overhaul of the nuclear power unit and during the outage of the main transformer, the operation mode during the diesel generator grid connection test is Mode 2;

[0051] When the power supply of standby power bus 1 is switched from line 1 to line 2 for operation, the operation mode is Mode 3;

[0052] When operating with a long-term tie-line as required by the power grid, the operation mode is Mode 4.

[0053] The following will be described in detail with several specific examples:

[0054] In the first example, during the grid connection operation of the nuclear power unit, the operation mode of the standby power supply system is Mode 1, which may specifically include:

[0055] During the grid connection operation of the nuclear power unit, the standby power supply system operates in Mode 1, with single-sided power supply adopted, and the line protection is switched to weak-signal response. When a 220 kV line trip occurs, the circuit breaker on the opposite side trips, and the circuit breaker on this side remains closed. If it is an instantaneous fault, the circuit breaker on the opposite side is immediately reclosed.

[0056] As Figure 1 shown, when operating in Mode 1: 220 kV line 1 is energized; 220 kV line 2 is energized; the circuit breakers 1 on the opposite side, circuit breaker 1 on this side, circuit breakers 2 on the opposite side, circuit breaker 2 on this side, circuit breaker 3, circuit breaker 4, circuit breaker 5, circuit breaker 6, circuit breaker 7, circuit breaker 8, and circuit breaker 9 are in the closed state; circuit breaker 10 and the bus-tie circuit breaker are in the open state; disconnecting switches 1, 3, 4, 6, and 7 are in the closed state; disconnecting switches 2, 5, and 8 are in the open state; the diesel generator is out of operation. With single-sided power supply adopted and the line protection switched to weak-signal response, when a 220 kV line fault occurs, circuit breaker 1 on the opposite side trips, and circuit breaker 1 on this side remains closed. If it is an instantaneous fault, circuit breaker 1 on the opposite side can be immediately reclosed to improve the reliability of line power supply.

[0057] In the second example, during the major overhaul or minor overhaul of the nuclear power unit and during the outage of the main transformer, the operation mode during the diesel generator grid connection test is Mode 2, which may specifically include:

[0058] During the major or minor overhaul of a nuclear power unit, when the main transformer is out of service, and during the diesel generator paralleling test, there will be two power sources: the 220 kV line and the diesel generator. In the case of double-sided power supply, it is necessary to switch from Mode 1 to Mode 2, trip the line protection, and deactivate the reclosing function. At this time, if a fault occurs, the circuit breakers on the opposite side and the local circuit breaker will trip simultaneously to eliminate the protection dead zone.

[0059] As Figure 1 shown, when operating in Mode 2: the 220 kV Line 1 is energized; the 220 kV Line 2 is energized; the circuit breakers on the opposite side 1, the local circuit breaker 1, the circuit breakers on the opposite side 2, the local circuit breaker 2, Circuit Breaker 3, Circuit Breaker 4, Circuit Breaker 5, Circuit Breaker 6, Circuit Breaker 7, Circuit Breaker 8, Circuit Breaker 9, and Circuit Breaker 10 are in the closed state; the diesel generator is operating in parallel; the bus-coupling circuit breaker is in the open state; Disconnecting Switch 1, Disconnecting Switch 3, Disconnecting Switch 4, Disconnecting Switch 6, and Disconnecting Switch 7 are in the closed state; Disconnecting Switch 2, Disconnecting Switch 5, and Disconnecting Switch 8 are in the open state. When operating in Mode 2, there will be two power sources: the 220 kV line and the diesel generator. In the case of double-sided power supply, it is necessary to trip the line protection and deactivate the reclosing function. At this time, if a fault occurs, the circuit breaker on the opposite side 1 and the local circuit breaker 2 will trip simultaneously to eliminate the protection dead zone and avoid equipment damage.

[0060] In the third example, when the power supply of the standby power bus 1 is switched from Line 1 to Line 2, the operating mode is Mode 3, which specifically may include:

[0061] When the standby power is operating in Mode 1 or Mode 2, if it is necessary to switch the power supply of the standby power bus 1 from Line 1 to Line 2, the operating mode can be switched to Mode 3; in this mode, the bus-coupling circuit breaker will be closed briefly, and the reclosing protection will be enabled. If the closed-loop state is maintained after the closed-loop operation, the operating mode will be adjusted to Mode 4; if the local circuit breaker of Line 1 is opened after the closed-loop operation, the mode will be changed back to Mode 1 or Mode 2.

[0062] When the standby power is operating in Mode 1 or Mode 2, if it is necessary to switch the power supply of the standby power bus 1 from Line 1 to Line 2, the operating mode can be switched to Mode 3. As Figure 1 shown, in this mode, during the switching: the 220 kV Line 1 is energized; the 220 kV Line 2 is energized; the circuit breakers on the opposite side 1, the local circuit breaker 1, the circuit breakers on the opposite side 2, the local circuit breaker 2, Circuit Breaker 3, Circuit Breaker 4, Circuit Breaker 5, Circuit Breaker 6, Circuit Breaker 7, Circuit Breaker 8, Circuit Breaker 9, and the bus-coupling circuit breaker are in the closed state; Circuit Breaker 10 is in the open state; Disconnecting Switch 1, Disconnecting Switch 2, Disconnecting Switch 3, Disconnecting Switch 4, Disconnecting Switch 6, and Disconnecting Switch 7 are in the closed state; Disconnecting Switch 5 and Disconnecting Switch 8 are in the open state; the diesel generator is out of service.

[0063] After the switching is completed: 220 kV Line 1 is in operation; 220 kV Line 2 is in operation; the opposite breaker 1, the local breaker 1, the opposite breaker 2, the local breaker 2, breaker 3, breaker 4, breaker 5, breaker 6, breaker 7, breaker 8, breaker 9 are in the closed state; the bus-coupler breaker and breaker 10 are in the open state; knife switch 2, knife switch 3, knife switch 4, knife switch 6, knife switch 7 are in the closed state; knife switch 1, knife switch 5, knife switch 8 are in the open state; the diesel engine is shut down.

[0064] Since the bus-coupler breaker will be closed briefly during the switching, in order to improve the reliability of the line power supply during this period, the reclosing protection is enabled to improve the power supply reliability. If the closed-loop state is continued after the closed-loop operation is completed, the operation mode is adjusted to Mode 4. If the local breaker of Line 1 needs to be opened after the closed-loop operation is completed, the mode is changed back to Mode 1 or Mode 2.

[0065] In the fourth example, at the request of the power grid, when the tie line is in long-term operation, the operation mode is Mode 4, which may specifically include:

[0066] At the request of the power grid, when the tie line is in long-term operation, the operation mode is Mode 4. In this mode, the closed-loop setting value is enabled, the line protection is set to trip, the backup protection is enabled, and the reclosing is enabled; after this operation condition ends, it is changed back to Mode 1.

[0067] At the request of the power grid, when the tie line is in long-term operation, the operation mode is Mode 4. In this mode, if Figure 1 As shown, 220 kV Line 1 is in operation; 220 kV Line 2 is in operation; the opposite breaker 1, the local breaker 1, the opposite breaker 2, the local breaker 2, breaker 3, breaker 4, breaker 5, breaker 6, breaker 7, breaker 8, breaker 9, the bus-coupler breaker are in the closed state; breaker 10 is in the open state; knife switch 1, knife switch 3, knife switch 4, knife switch 6, knife switch 7 are in the closed state; knife switch 2, knife switch 5, knife switch 8 are in the open state; the diesel engine is shut down.

[0068] Since the bus-coupler breaker will be closed for a long time, it is necessary to enable the closed-loop setting value, set the line protection to trip, enable the backup protection, and enable the reclosing. After this operation condition ends, it can be changed back to Mode 1.

[0069] A control method for multi - mode operation of the standby power supply system of a nuclear power unit provided by an embodiment of the present application provides various combinations of operating modes for the standby power supply of a nuclear power plant, making the operation modes of in - station equipment flexible; facilitating the production operation dispatching management of the power grid; and improving the reliability of the standby power supply system. Relay protection adjustment schemes are proposed for different operating conditions, improving the success rate of reclosing in case of high - voltage line faults during single - side power supply; effectively avoiding protection dead zones and preventing equipment damage during double - side power supply; and using operators to make accurate judgments to improve the success rate of mode switching.

[0070] Based on the control method for multi - mode operation of the standby power supply system of a nuclear power unit provided by the above - mentioned embodiment, an embodiment of the present application provides a control device for multi - mode operation of the standby power supply system of a nuclear power unit.

[0071] See Figure 3 , which is a schematic structural diagram of a control device for multi - mode operation of the standby power supply system of a nuclear power unit provided by an embodiment of the present application.

[0072] A control device for multi - mode operation of the standby power supply system of a nuclear power unit provided by an embodiment of the present application includes:

[0073] A mode determination module 100, configured to determine multiple operating modes of the standby power supply system;

[0074] A mode switching module 200, configured to select a corresponding operating mode from multiple operating modes according to the operating conditions of the nuclear power unit under different conditions.

[0075] The above - mentioned embodiments of the present application are described in detail in combination with the accompanying drawings, but the present application is not limited to the above - mentioned embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the purpose of the present application. The content not described in detail in the present application can all adopt the prior art.

Claims

1. A control method for multi-mode operation of an emergency power supply system of a nuclear power unit, characterized in that, The method includes: Determine multiple operating modes of the backup power supply system; According to the operating conditions of the nuclear power unit, select the corresponding operating mode from the multiple operating modes under different conditions; The multiple operating modes include: Mode 1: Unilateral power supply operating mode, with weak current response enabled for line protection; Mode 2: Bilateral power supply operating mode, with line protection set to trip and reclosing disabled; Mode 3: Short-term tie line power supply operating mode, with normal setting values enabled, line protection set to trip, and reclosing enabled; Mode 4: Long-term tie line power supply operating mode, with loop closing setting values enabled, line protection set to trip, backup protection enabled, and reclosing enabled; The step of selecting the corresponding operating mode from the multiple operating modes according to the operating conditions of the nuclear power unit specifically includes: During the grid-connected operation of the nuclear power unit, the operating mode of the backup power supply system is Mode 1; During the major or minor overhaul of the nuclear power unit, when the main transformer is out of service, and during the diesel generator grid connection test, the operating mode is Mode 2; When the power supply of backup power bus 1 is switched from line 1 to line 2 for operation, the operating mode is Mode 3; When required by the power grid to operate with a long-term tie line, the operating mode is Mode 4; The statement that during the grid-connected operation of the nuclear power unit, the operating mode of the backup power supply system is Mode 1 specifically includes: During the grid-connected operation of the nuclear power unit, the backup power supply system operates in Mode 1, with unilateral power supply, weak current response enabled for line protection. When a 220 kV line trip occurs, the circuit breaker on the opposite side trips, and the circuit breaker on this side remains closed. If it is an instantaneous fault, the circuit breaker on the opposite side is immediately reclosed; The statement that during the major or minor overhaul of the nuclear power unit, when the main transformer is out of service, and during the diesel generator grid connection test, the operating mode is Mode 2 specifically includes: During the major or minor overhaul of the nuclear power unit, when the main transformer is out of service, and during the diesel generator grid connection test, there will be two power sources: the 220 kV line and the diesel generator. In the case of bilateral power supply, it is necessary to switch from Mode 1 to Mode 2, set the line protection to trip, and disable the reclosing. At this time, if a fault occurs, the circuit breakers on both the opposite side and this side will trip simultaneously to eliminate the protection dead zone; The statement that when the power supply of backup power bus 1 is switched from line 1 to line 2 for operation, the operating mode is Mode 3 specifically includes: When the backup power supply operates in Mode 1 or Mode 2, if it is necessary to switch the power supply of backup power bus 1 from line 1 to line 2 for operation, the operating mode can be switched to Mode 3; in this mode, the bus tie breaker will be closed briefly, and the reclosing protection will be enabled. If the loop closing state is maintained after the loop closing operation, the operating mode will be adjusted to Mode 4; if the circuit breaker on this side of line 1 is opened after the loop closing, the mode will be changed back to Mode 1 or Mode 2; The statement that when required by the power grid to operate with a long-term tie line, the operating mode is Mode 4 specifically includes: When required by the power grid to operate with a long-term tie line, the operating mode is Mode 4. In this mode, the loop closing setting values are enabled, the line protection is set to trip, the backup protection is enabled, and the reclosing is enabled; after this operating condition ends, it is changed back to Mode 1.

2. A control device for multi-mode operation of an emergency power supply system of a nuclear power unit, characterized in that, The device includes: A mode determination module for determining multiple operating modes of the standby power supply system; A mode switching module for selecting a corresponding operating mode from the multiple operating modes according to the operating conditions of the nuclear power unit under different conditions; The multiple operating modes include: Mode 1: Single-sided power supply operating mode, with weak current response for line protection; Mode 2: Double-sided power supply operating mode, with line protection tripping and reclosing disabled; Mode 3: Short-term tie line power supply operating mode, with normal settings enabled, line protection tripping, and reclosing enabled; Mode 4: Long-term tie line power supply operating mode, with loop closing settings enabled, line protection tripping, backup protection enabled, and reclosing enabled; The selecting a corresponding operating mode from the multiple operating modes according to the operating conditions of the nuclear power unit under different conditions specifically includes: During the grid-connected operation of the nuclear power unit, the operating mode of the standby power supply system is Mode 1; During the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, the operating mode is Mode 2; When the power supply of standby power bus 1 is switched from line 1 to line 2 for operation, the operating mode is Mode 3; At the request of the power grid, when using the tie line for long-term operation, the operating mode is Mode 4; The during the grid-connected operation of the nuclear power unit, the operating mode of the standby power supply system is Mode 1 specifically includes: During the grid-connected operation of the nuclear power unit, the standby power supply system operates in Mode 1, with single-sided power supply, weak current response for line protection. When a 220 kV line trips, the circuit breaker on the opposite side trips, and the circuit breaker on the local side remains closed. If it is an instantaneous fault, the circuit breaker on the opposite side is immediately reclosed; The during the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, the operating mode is Mode 2 specifically includes: During the major or minor overhaul of the nuclear power unit, during the outage of the main transformer, and during the diesel generator grid connection test, there will be two power sources, namely the 220 kV line and the diesel generator. In the case of double-sided power supply, it is necessary to switch from Mode 1 to Mode 2, with line protection tripping and reclosing disabled. At this time, if a fault occurs, the circuit breakers on the opposite side and the local side will trip simultaneously to eliminate the protection dead zone; The when the power supply of standby power bus 1 is switched from line 1 to line 2 for operation, the operating mode is Mode 3 specifically includes: When the standby power supply operates in Mode 1 or Mode 2, if it is necessary to switch the power supply of standby power bus 1 from line 1 to line 2 for operation, the operating mode can be switched to Mode 3; in this mode, the bus-tie circuit breaker will be closed briefly, and the reclosing protection will be enabled. If the loop closing state is maintained after the loop closing operation, the operating mode will be adjusted to Mode 4; if the local circuit breaker of line 1 is opened after the loop closing, the mode will be changed back to Mode 1 or Mode 2; The at the request of the power grid, when using the tie line for long-term operation, the operating mode is Mode 4 specifically includes: At the request of the power grid, when using the tie line for long-term operation, the operating mode is Mode 4. In this mode, the loop closing settings are enabled, the line protection is tripped, the backup protection is enabled, and the reclosing is enabled; after this operating condition ends, it is changed back to Mode 1.

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