A method for reconstructing a dc system of a two-thirds wiring nuclear power switch station

Abstract

The present application relates to the technical field of nuclear power switch station DC system reconstruction, and specifically provides a two-thirds wiring nuclear power switch station DC system reconstruction method, which comprises the following steps: putting new DC system main equipment into operation and carrying out no-load operation, and pre-laying DC feeder cable; classifying and corresponding switch station DC load to public equipment, main transformer equipment, line equipment, bus equipment and circuit breaker equipment; transferring DC power supply of the public equipment to the new DC system; performing power-off operation on the main transformer equipment, line equipment, bus equipment and circuit breaker equipment, and connecting the corresponding DC load to the new DC system; and removing the old DC system to complete the nuclear power switch station DC system reconstruction. The method provided by the present application greatly shortens the DC system reconstruction period without affecting the conventional external power supply of the switch station and ensuring safety, and meets the dual requirements of safety and reconstruction period of the nuclear power switch station.

Description

Technical Field

[0001] This invention relates to the field of DC system retrofitting technology for nuclear power plant switchyards, and in particular to a method for retrofitting a DC system in a nuclear power plant switchyard with a three-way connection. Background Technology

[0002] The switchyard of a nuclear power plant is the core hub for power output. Its DC system, including battery banks and DC power cabinets, bears the heavy responsibility of supplying power to secondary electrical equipment such as GIS control equipment, protection equipment, remote control equipment, safety automation equipment, and metering equipment in the switchyard.

[0003] The DC systems of early-operation nuclear power plant switchyards have been running for many years, and the original DC system equipment is outdated and cannot fully meet the requirements of current regulations and standards, posing certain operational risks. With the ongoing extension of nuclear power plant lifespans, these early-operational switchyards face the need to replace their DC systems. To avoid disrupting power supply, the nuclear power plant switchyards cannot be completely shut down; therefore, simply replacing equipment after a power outage is not a viable method for upgrading the DC systems.

[0004] There are many existing methods for retrofitting DC systems. Based on the different key steps they involve, they can be mainly categorized as follows: 1) Installing a temporary transition DC power supply panel: This method involves two load transfers, which inevitably require short-term power outages of multiple feeder branches on the feeder panel to connect to the new DC system. This method cannot avoid short-term power outages of a large number of DC feeder circuits and the need for DC loads (such as protection cabinets) to be temporarily taken out of operation, posing safety hazards.

[0005] 2) Interconnection and parallel operation of new and old DC systems: This method may cause circulating current or face operational risks such as decreased sensitivity of DC system ground fault detection.

[0006] 3) Load Transfer by Power Outage: After the new DC system is built, power outages are implemented in rotation for each bay to complete the load transfer. This method is highly safe and can achieve a thorough transformation, but if the rotational power outages for each bay are not properly planned, too many outage windows will be required, and the transformation cycle will be too long. Figure 1 Taking a typical 3 / 2 wiring as an example, this wiring includes 2 busbar bays, 6 circuit breaker bays, 2 outgoing line bays, and 2 main transformer incoming line bays. If a single bay is de-energized in turn, 12 power outage windows are required, and such a renovation cycle is obviously unacceptable.

[0007] In summary, existing DC system retrofitting methods cannot simultaneously meet the dual requirements of safety and retrofitting time for nuclear power switchyards. It is necessary to provide a three-half connection nuclear power switchyard DC system retrofitting method to solve the above-mentioned technical problems. Summary of the Invention

[0008] The main objective of this invention is to provide a method for retrofitting the DC system of a two-thirds-connected nuclear power plant switchyard, which shortens the retrofitting cycle while meeting the safety requirements of the nuclear power plant switchyard. The specific technical solution is as follows: A method for retrofitting the DC system of a nuclear power plant switchyard with a three-way connection includes the following steps: S1. Put the main equipment of the new DC system into operation and run it under no-load, and pre-lay the DC feeder cables; classify the DC loads of the switch station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, wherein the circuit breaker equipment includes side circuit breaker equipment and interrupted circuit breaker equipment. S2. Coordinate with the dispatch center to agree on a short-term implementation window to transfer the DC power supply of public equipment to the new DC system; S3. Perform a power outage operation on the main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, and connect the corresponding DC loads to the new DC system; The power outage operation includes: performing a first power outage operation; and performing a second power outage operation after performing the first power outage operation; wherein the first power outage operation is any one of the following two schemes: Power off the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment; Power outage of the main transformer side busbar equipment, all side circuit breaker equipment connected to the busbar equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string; The second power outage operation is to de-energize the remaining equipment that was not de-energized in the first power outage operation; S4. Dismantle the old DC system and complete the DC system upgrade of the nuclear power plant switchyard.

[0009] Furthermore, when the first power outage operation is to de-energize the line-side busbar equipment and all circuit breaker equipment connected to the busbar equipment, the second power outage operation is: Using the maintenance window of one of the main transformer line strings, de-energize the main transformer equipment, line equipment, circuit breaker equipment, main transformer side bus equipment, and all side circuit breaker equipment connected to the main transformer side bus equipment in that string. Using the maintenance window of another main transformer line string, de-energize the main transformer equipment, line equipment, and circuit breaker equipment in that string. When the first power outage operation is to de-energize the main transformer side busbar equipment, all side circuit breaker equipment connected to the busbar equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string, the second power outage operation is: Power off the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment; Using the maintenance window of another main transformer line string, de-energize the main transformer equipment, line equipment, and circuit breaker equipment in that string.

[0010] Furthermore, S1 includes the following steps: S1.1 Install a new DC system and arrange the battery pack, DC charging panel, DC feeder panel and DC bus tie panel of the DC system in place; S1.2 Debugging equipment: Put the part of the new DC system, except for the DC feeder panel, into operation first. All feeder switches of the new DC system are in the open position. At this time, the new DC system is in an unloaded state. S1.3. Pre-lay the DC feeder cable to the cabinet that requires DC power supply; S1.4 Classify all loads requiring DC power supply in the switching station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment, and circuit breaker equipment.

[0011] Furthermore, the structure of the three-way connection nuclear power switch station is as follows: two main transformer line strings are set up. Each main transformer line string includes an incoming line circuit breaker 1DL, an interrupt circuit breaker 2DL, and an outgoing line circuit breaker 3DL connected in series between bus I and bus II. Isolating switches 11G and 12G are respectively installed at both ends of the incoming line circuit breaker 1DL; isolating switches 21G and 22G are respectively installed at both ends of the interrupt circuit breaker 2DL; and isolating switches 31G and 32G are respectively installed at both ends of the outgoing line circuit breaker 3DL. The main transformer equipment and the line equipment are each equipped with two sets, each corresponding to two main transformer line strings; The busbar equipment includes main transformer-side busbar equipment and line-side busbar equipment, corresponding to the main transformer-side busbar and the line-side busbar, respectively; The circuit breaker equipment includes side circuit breaker equipment and interrupt circuit breaker equipment. The side circuit breaker equipment is provided in four sets, corresponding to the incoming side circuit breaker 1DL and the outgoing side circuit breaker 3DL respectively. The interrupt circuit breaker equipment is provided in two sets, corresponding to the interrupt circuit breaker 2DL respectively.

[0012] Furthermore, in S3, the specific operation of de-energizing the line-side busbar equipment and all circuit breaker equipment connected to the busbar equipment, and connecting the corresponding DC loads to the new DC system includes the following steps: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. Disconnect the 3DL, 32G, and 31G of the first main transformer line string in sequence, and then disconnect the 1DL, 11G, and 12G of the second main transformer line string to take bus II out of operation. Deactivate the circuit breaker protection of 3DL for the first main transformer line string and 1DL for the second main transformer line string, and deactivate the bus protection of Bus II. The DC power supply of the circuit breaker equipment corresponding to the 3DL of the first main transformer line string, the 1DL of the second main transformer line string, and the line-side bus equipment corresponding to the II bus is transferred to the new DC system. The first main transformer line string 31G, 32G, 3DL and the second main transformer line string 12G, 11G, 1DL are combined, the II bus is put into operation, and the complete string operation is restored. Activate the circuit breaker protection of 3DL in the first main transformer line string, the circuit breaker protection of 1DL in the second main transformer line string, and activate the bus protection of II bus.

[0013] Furthermore, the specific operation of de-energizing the main transformer side bus equipment, all side circuit breaker equipment connected to the bus equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string, and connecting the corresponding DC loads to the new DC system includes the following steps: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. The maintenance windows of the main transformer and the line maintenance windows of the first main transformer line string are arranged synchronously. The 2DL of the first main transformer line string is disconnected and the circuit breaker 2DL is disconnected from the first main transformer line string. Disconnect 3DL, 31G, and 32G of the first main transformer line string in sequence, and the outgoing terminal circuit breaker of the first main transformer line string is taken out of operation. When the #1 main transformer is out of service, disconnect 1DL and 12G of the first main transformer line string in sequence, and cold standby circuit breaker at the incoming end of the first main transformer line string; disconnect 22G and 21G of the first main transformer line string in sequence, and completely isolate circuit breaker 2DL from the first main transformer line string. Disconnect 3DL and 32G of the second main transformer line string and 11G of the first main transformer line string, and the I bus will exit operation; disconnect 31G of the second main transformer line string, and the 3DL of the second main transformer line string will exit operation. Withdraw the circuit breaker protection of 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string; withdraw the line protection of outgoing line 1, bus protection of I bus, protection of #1 main transformer, and protection of T zone of the first main transformer line string. The DC power supply of the circuit breaker equipment corresponding to 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string, the main transformer side bus equipment corresponding to I bus, and the line equipment corresponding to the first main transformer line string are transferred to the new DC system. Put bus I into operation, put main transformer #1 into operation, connect the 2DL and 3DL of the first main transformer line string, and put outgoing line 1 into operation; restore the circuit breaker protection of the 1DL and 2DL of the first main transformer line string and the 3DL of the second main transformer line string, and restore the protection of bus I, main transformer #1, outgoing line 1, and the T-zone protection of the first main transformer line string.

[0014] Furthermore, using another main transformer line maintenance window, the main transformer equipment, line equipment, and circuit breaker equipment in that string are de-energized, and the corresponding DC loads are connected to the new DC system. The specific operation includes the following steps: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. Synchronize the maintenance windows of the main transformer and the line maintenance windows of the second main transformer line string, disconnect the 2DL of the second main transformer line string, and disconnect the circuit breaker 2DL from the second main transformer line string. #2 main transformer is out of service. 1DL, 12G and 11G of the second main transformer line string are disconnected in sequence. Bus II is operating normally. Outgoing line 2 is out of service. The 3DL, 31G, 32G, 21G, and 22G lines of the second main transformer line string are disconnected in sequence. Bus I is operating normally. Exit #2 main transformer protection, outgoing line 2 line protection, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string; The DC power supply of the circuit breaker equipment corresponding to 2DL of the second main transformer line string, the main transformer equipment and line equipment corresponding to the second main transformer line string is transferred to the new DC system. Connect the 32G, 31G, and 1DL of the second main transformer line string, and put the #2 main transformer into operation; connect the 21G, 22G, and 2DL of the second main transformer line string, and put the circuit breaker into operation; put outgoing line 2 into operation; Restore the protection of main transformer #2, outgoing line 2, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string.

[0015] Furthermore, the low-frequency disconnection panel, protection and fault information substation panel, remote communication panel, power acquisition panel, network communication panel, AVC panel, GPS time synchronization device panel, PMU host panel, and 380V switchgear control power supply DC load are classified and mapped to common equipment. Classify and map the DC loads of the main transformer bay control cabinet, the main transformer incoming line T-zone protection cabinet, and the unit interface cabinet to the main transformer equipment. Classify and map the DC loads of line protection cabinets, line bay control cabinets, and line outgoing T-zone protection cabinets to the line equipment. Classify and map the DC loads of circuit breaker protection cabinets, circuit breaker measurement and control cabinets, and circuit breaker bay control cabinets to circuit breaker equipment. The DC loads of busbar protection cabinets, busbar monitoring and control panels, and busbar bay control cabinets are classified and mapped to busbar equipment.

[0016] The beneficial effects achieved by this solution are: The present invention provides a method for retrofitting the DC system of a 3 / 2 wiring nuclear power plant switchyard. Addressing the high safety requirements of nuclear power plant switchyard retrofitting, and to avoid disrupting the switchyard's regular external power supply while mitigating safety hazards such as short-term power outages of numerous DC feeder circuits during load transfer and the temporary shutdown of DC loads like protection cabinets, this method optimizes existing methods. Considering implementation difficulty and reducing repeated switching operations, it combines bay maintenance windows and determines the implementation sequence based on the wiring characteristics, thereby shortening the overall DC system retrofit cycle and ensuring a safe and thorough retrofit. For this typical 3 / 2 wiring configuration, previously 12 partial power outages were required per bay; after optimization, the entire DC load transfer can be completed within three major overhaul windows, significantly shortening the retrofit cycle. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a two-string bay in a nuclear power plant switchyard with a three-way connection.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0022] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0025] Example 1: This invention proposes a method for retrofitting the DC system of a three-half-connected nuclear power plant switchyard, comprising the following steps: S1. Put the main equipment of the new DC system into operation and run it under no-load, and pre-lay the DC feeder cables; classify the DC loads of the switch station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, wherein the circuit breaker equipment includes side circuit breaker equipment and interrupted circuit breaker equipment. S1 includes the following steps: S1.1 Install a new DC system and arrange the battery pack, DC charging panel, DC feeder panel and DC bus tie panel of the DC system in place; S1.2 Debugging equipment: Put the part of the new DC system, except for the DC feeder panel, into operation first. All feeder switches of the new DC system are in the open position. At this time, the new DC system is in an unloaded state. S1.3. Pre-lay the DC feeder cable to the cabinet that requires DC power supply; S1.4 Classify all loads requiring DC power supply in the switching station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment, and circuit breaker equipment.

[0026] In this embodiment, the DC loads of common equipment within the substation area, such as low-frequency disconnection panels, protection and fault information substation panels, remote communication panels, power acquisition panels, network communication panels, AVC panels, GPS time synchronization equipment panels, PMU host panels, and 380V switchgear control power supplies, are classified and associated with common equipment. Within the switchyard area, DC loads related to the main transformer, such as the main transformer bay control cabinet, the main transformer incoming line T-zone protection cabinet, and the unit interface cabinet, are classified and corresponding to the main transformer equipment. DC loads related to the line within the switching station area, such as line protection cabinets, line bay control cabinets, and line outgoing T-zone protection cabinets, are classified and corresponding to line equipment. Within the switching station area, DC loads related to circuit breakers, such as circuit breaker protection cabinets, circuit breaker measurement and control cabinets, and circuit breaker bay control cabinets, are classified and corresponding to circuit breaker equipment. DC loads related to the busbar within the switchyard area, such as busbar protection cabinets, busbar monitoring and control panels, and busbar bay control cabinets, are classified and corresponding to busbar equipment.

[0027] S2. Coordinate with the dispatch center to agree on a short-term implementation window to transfer the DC power supply of public equipment to the new DC system; S3. Perform a power outage operation on the main transformer equipment, line equipment, busbar equipment, and circuit breaker equipment, and connect the corresponding DC loads to the new DC system; specifically including: S3.1 De-energize the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment, and connect the corresponding DC load to the new DC system; S3.2. Using the maintenance window of one of the main transformer line strings, de-energize the main transformer equipment, line equipment, circuit breaker equipment, main transformer side bus equipment, and all side circuit breaker equipment connected to the main transformer side bus equipment in that string, and connect the corresponding DC load to the new DC system. S3.3. Using the maintenance window of another main transformer line string, de-energize the main transformer equipment, line equipment and circuit breaker equipment of that string, and connect the corresponding DC load to the new DC system.

[0028] The following describes the DC system modification method based on the specific structure of a three-half-connected nuclear power switchyard.

[0029] See Figure 1 The structure of the three-half-connected nuclear power switch station is as follows: two main transformer line strings are set up (the specific number can be adjusted according to the actual situation; for the sake of convenience, only two main transformer line strings are shown in this embodiment). The one on the left is the first main transformer line string, and the one on the right is the second main transformer line string. Each main transformer line string includes an incoming line circuit breaker 1DL, an interrupt circuit breaker 2DL, and an outgoing line circuit breaker 3DL connected in series between bus I and bus II.

[0030] In the first main transformer line string, the incoming circuit breaker 1DL is connected to Bus I, and the outgoing circuit breaker 3DL is connected to Bus II. The two ends of the incoming circuit breaker 1DL are equipped with isolating switches 11G and 12G respectively, with isolating switch 11G on the Bus I side. The two ends of the circuit breaker 2DL are equipped with isolating switches 21G and 22G respectively, with isolating switch 21G on the Bus I side. The two ends of the outgoing circuit breaker 3DL are equipped with isolating switches 31G and 32G respectively, with isolating switch 31G on the Bus I side. Main transformer incoming line 1 is connected between 12G and 21G, and outgoing line 1 is connected between 22G and 31G. Main transformer #1 is connected to main transformer incoming line 1.

[0031] In the second main transformer line string, the incoming circuit breaker 1DL is connected to bus II, and the outgoing circuit breaker 3DL is connected to bus I. The two ends of the incoming circuit breaker 1DL are equipped with isolating switches 11G and 12G respectively, with isolating switch 11G on the side of bus II. The two ends of the circuit breaker 2DL are equipped with isolating switches 21G and 22G respectively, with isolating switch 21G on the side of bus II. The two ends of the outgoing circuit breaker 3DL are equipped with isolating switches 31G and 32G respectively, with isolating switch 31G on the side of bus II. The main transformer incoming line 2 is connected between 12G and 21G, and the outgoing line 2 is connected between 22G and 31G. The #2 main transformer is connected to the main transformer incoming line 2.

[0032] The main transformer equipment and the line equipment are each equipped with two sets, each corresponding to two main transformer line strings; The bus equipment includes main transformer-side bus equipment and line-side bus equipment, which correspond to the main transformer-side bus and the line-side bus, respectively. In the first main transformer line string, the main transformer-side bus equipment corresponds to bus I and the line-side bus equipment corresponds to bus II. In the second main transformer line string, the main transformer-side bus equipment corresponds to bus II and the line-side bus equipment corresponds to bus I. The circuit breaker equipment includes side circuit breaker equipment and interrupt circuit breaker equipment. The side circuit breaker equipment is provided in four sets, corresponding to the incoming side circuit breaker 1DL and the outgoing side circuit breaker 3DL respectively. The interrupt circuit breaker equipment is provided in two sets, corresponding to the interrupt circuit breaker 2DL respectively.

[0033] In this embodiment, the first main transformer line string is used as an example for illustration. The specific operation includes the following steps: S3.1 Check the status before operation. Both main transformer line strings are running as complete strings, and the protection is operating normally. Disconnect the 3DL, 32G, and 31G of the first main transformer line string in sequence, and then disconnect the 1DL, 11G, and 12G of the second main transformer line string to take bus II out of operation. Deactivate the circuit breaker protection of 3DL for the first main transformer line string and 1DL for the second main transformer line string, and deactivate the bus protection of Bus II. The DC power supply of the circuit breaker equipment corresponding to the 3DL of the first main transformer line string, the 1DL of the second main transformer line string, and the line-side bus equipment corresponding to the II bus is transferred to the new DC system. The first main transformer line string 31G, 32G, 3DL and the second main transformer line string 12G, 11G, 1DL are combined, the II bus is put into operation, and the complete string operation is restored. Activate the circuit breaker protection of 3DL in the first main transformer line string, the circuit breaker protection of 1DL in the second main transformer line string, and activate the bus protection of II bus.

[0034] S3.2 Check the status before operation. Both main transformer line strings are running as complete strings, and the protection is operating normally. The maintenance windows of the main transformer and the line maintenance windows of the first main transformer line string are arranged synchronously. The 2DL of the first main transformer line string is disconnected and the circuit breaker 2DL is disconnected from the first main transformer line string. Disconnect 3DL, 31G, and 32G of the first main transformer line string in sequence, and the outgoing terminal circuit breaker of the first main transformer line string is taken out of operation. When the #1 main transformer is out of service, disconnect 1DL and 12G of the first main transformer line string in sequence, and cold standby circuit breaker at the incoming end of the first main transformer line string; disconnect 22G and 21G of the first main transformer line string in sequence, and completely isolate circuit breaker 2DL from the first main transformer line string. Disconnect 3DL and 32G of the second main transformer line string and 11G of the first main transformer line string, and the I bus will exit operation; disconnect 31G of the second main transformer line string, and the 3DL of the second main transformer line string will exit operation. Withdraw the circuit breaker protection of 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string; withdraw the line protection of outgoing line 1, bus protection of I bus, protection of #1 main transformer, and protection of T zone of the first main transformer line string. The DC power supply of the circuit breaker equipment corresponding to 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string, the main transformer side bus equipment corresponding to I bus, and the line equipment corresponding to the first main transformer line string are transferred to the new DC system. Put bus I into operation, put main transformer #1 into operation, connect the 2DL and 3DL of the first main transformer line string, and put outgoing line 1 into operation; restore the circuit breaker protection of the 1DL and 2DL of the first main transformer line string and the 3DL of the second main transformer line string, and restore the protection of bus I, main transformer #1, outgoing line 1, and the T-zone protection of the first main transformer line string.

[0035] S3.3 Check the status before operation. Both main transformer line strings are running as complete strings, and the protection is operating normally. Synchronize the maintenance windows of the main transformer and the line maintenance windows of the second main transformer line string, disconnect the 2DL of the second main transformer line string, and disconnect the circuit breaker 2DL from the second main transformer line string. #2 main transformer is out of service. 1DL, 12G and 11G of the second main transformer line string are disconnected in sequence. Bus II is operating normally. Outgoing line 2 is out of service. The 3DL, 31G, 32G, 21G, and 22G lines of the second main transformer line string are disconnected in sequence. Bus I is operating normally. Exit #2 main transformer protection, outgoing line 2 line protection, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string; The DC power supply of the circuit breaker equipment corresponding to 2DL of the second main transformer line string, the main transformer equipment and line equipment corresponding to the second main transformer line string is transferred to the new DC system. Connect the 32G, 31G, and 1DL of the second main transformer line string, and put the #2 main transformer into operation; connect the 21G, 22G, and 2DL of the second main transformer line string, and put the circuit breaker into operation; put outgoing line 2 into operation; Restore the protection of main transformer #2, outgoing line 2, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string.

[0036] S4. Dismantle the old DC system and complete the DC system upgrade of the nuclear power plant switchyard.

[0037] Example 2: This embodiment proposes a method for retrofitting the DC system of a three-way connected nuclear power plant switchyard, including the following steps: S1. Put the main equipment of the new DC system into operation and run it under no-load, and pre-lay the DC feeder cables; classify the DC loads of the switch station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, wherein the circuit breaker equipment includes side circuit breaker equipment and interrupted circuit breaker equipment.

[0038] S2. Coordinate with the dispatch center to agree on a short-term implementation window to transfer the DC power supply of public equipment to the new DC system.

[0039] S3. Perform a power outage operation on the main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, and connect the corresponding DC loads to the new DC system; S3.1 De-energize the main transformer side busbar equipment, all side circuit breaker equipment connected to the busbar equipment, as well as the circuit breaker equipment, line equipment and main transformer equipment of a single main transformer line string; S3.2 De-energize the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment; S3.3. Using another main transformer line maintenance window, de-energize the main transformer equipment, line equipment, and circuit breaker equipment in that string.

[0040] S4. Dismantle the old DC system and complete the DC system upgrade of the nuclear power plant switchyard.

[0041] The only difference between this embodiment and Embodiment 1 is the order of S3.1 and S3.2; all other operations are the same and will not be repeated here.

[0042] The present invention provides a method for retrofitting the DC system of a 3 / 2 wiring nuclear power plant switchyard. Addressing the high safety requirements of nuclear power plant switchyard retrofitting, and to avoid disrupting the switchyard's regular external power supply while mitigating safety hazards such as short-term power outages of numerous DC feeder circuits during load transfer and the temporary shutdown of DC loads like protection cabinets, this method optimizes existing methods. Considering implementation difficulty and reducing repeated switching operations, it combines bay maintenance windows and determines the implementation sequence based on the wiring characteristics, thereby shortening the overall DC system retrofit cycle and ensuring a safe and thorough retrofit. For this typical 3 / 2 wiring configuration, previously 12 partial power outages were required per bay; after optimization, the entire DC load transfer can be completed within three major overhaul windows, significantly shortening the retrofit cycle.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for retrofitting the DC system of a three-half-connected nuclear power plant switchyard, characterized in that, Includes the following steps: S1. Put the main equipment of the new DC system into operation and run it under no-load, and pre-lay the DC feeder cables; classify the DC loads of the switch station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, wherein the circuit breaker equipment includes side circuit breaker equipment and interrupted circuit breaker equipment. S2. Coordinate with the dispatch center to agree on a short-term implementation window to transfer the DC power supply of public equipment to the new DC system; S3. Perform a power outage operation on the main transformer equipment, line equipment, busbar equipment and circuit breaker equipment, and connect the corresponding DC loads to the new DC system; The power outage operation includes: performing a first power outage operation; and performing a second power outage operation after performing the first power outage operation; wherein the first power outage operation is any one of the following two schemes: Power off the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment; Power outage of the main transformer side busbar equipment, all side circuit breaker equipment connected to the busbar equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string; The second power outage operation is to de-energize the remaining equipment that was not de-energized in the first power outage operation; S4. Dismantle the old DC system and complete the DC system upgrade of the nuclear power plant switchyard.

2. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 1, characterized in that, When the first power outage operation is to de-energize the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment, the second power outage operation is: Using the maintenance window of one of the main transformer line strings, de-energize the main transformer equipment, line equipment, circuit breaker equipment, main transformer side bus equipment, and all side circuit breaker equipment connected to the main transformer side bus equipment in that string. Using the maintenance window of another main transformer line string, de-energize the main transformer equipment, line equipment, and circuit breaker equipment in that string. When the first power outage operation is to de-energize the main transformer side busbar equipment, all side circuit breaker equipment connected to the busbar equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string, the second power outage operation is: Power off the line-side busbar equipment and all side circuit breaker equipment connected to the busbar equipment; Using the maintenance window of another main transformer line string, de-energize the main transformer equipment, line equipment, and circuit breaker equipment in that string.

3. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 2, characterized in that, S1 includes the following steps: S1.1 Install a new DC system and arrange the battery pack, DC charging panel, DC feeder panel, and DC bus tie panel of the DC system in place; S1.2 Debugging equipment: Put the part of the new DC system, except for the DC feeder panel, into operation first. All feeder switches of the new DC system are in the open position. At this time, the new DC system is in an unloaded state. S1.

3. Pre-lay the DC feeder cable to the cabinet that requires DC power supply; S1.4 Classify all loads requiring DC power supply in the switching station and assign them to public equipment, main transformer equipment, line equipment, busbar equipment, and circuit breaker equipment.

4. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 3, characterized in that, The structure of the three-half connection nuclear power switchyard is as follows: two main transformer line strings are set up. Each main transformer line string includes an incoming line circuit breaker 1DL, an interrupt circuit breaker 2DL, and an outgoing line circuit breaker 3DL connected in series between bus I and bus II. The two ends of the incoming line circuit breaker 1DL are respectively equipped with isolating switches 11G and 12G; the two ends of the interrupt circuit breaker 2DL are respectively equipped with isolating switches 21G and 22G; and the two ends of the outgoing line circuit breaker 3DL are respectively equipped with isolating switches 31G and 32G. The main transformer equipment and the line equipment are each equipped with two sets, each corresponding to two main transformer line strings; The busbar equipment includes main transformer-side busbar equipment and line-side busbar equipment, corresponding to the main transformer-side busbar and the line-side busbar, respectively; The circuit breaker equipment includes side circuit breaker equipment and interrupt circuit breaker equipment. The side circuit breaker equipment is provided in four sets, corresponding to the incoming side circuit breaker 1DL and the outgoing side circuit breaker 3DL respectively. The interrupt circuit breaker equipment is provided in two sets, corresponding to the interrupt circuit breaker 2DL respectively.

5. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 4, characterized in that, In S3, the specific operation of de-energizing the line-side busbar equipment and all circuit breaker equipment connected to the busbar equipment, and connecting the corresponding DC loads to the new DC system includes the following steps: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. Disconnect the 3DL, 32G, and 31G of the first main transformer line string in sequence, and then disconnect the 1DL, 11G, and 12G of the second main transformer line string to take bus II out of operation. Deactivate the circuit breaker protection of 3DL for the first main transformer line string and 1DL for the second main transformer line string, and deactivate the bus protection of Bus II. The DC power supply of the circuit breaker equipment corresponding to the 3DL of the first main transformer line string, the 1DL of the second main transformer line string, and the line-side bus equipment corresponding to the II bus is transferred to the new DC system. The first main transformer line string 31G, 32G, 3DL and the second main transformer line string 12G, 11G, 1DL are combined, the II bus is put into operation, and the complete string operation is restored. Activate the circuit breaker protection of 3DL in the first main transformer line string, the circuit breaker protection of 1DL in the second main transformer line string, and activate the bus protection of II bus.

6. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 4, characterized in that, The specific steps for de-energizing the main transformer side bus equipment, all side circuit breaker equipment connected to the bus equipment, and the circuit breaker equipment, line equipment, and main transformer equipment of a single main transformer line string, and connecting the corresponding DC loads to the new DC system, include the following: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. The maintenance windows of the main transformer and the line maintenance windows of the first main transformer line string are arranged synchronously. The 2DL of the first main transformer line string is disconnected and the circuit breaker 2DL is disconnected from the first main transformer line string. Disconnect 3DL, 31G, and 32G of the first main transformer line string in sequence, and the outgoing terminal circuit breaker of the first main transformer line string is taken out of operation. #1 main transformer out of service, disconnect 1DL and 12G of the first main transformer line string in sequence, and cold standby circuit breaker at the incoming end of the first main transformer line string. Disconnect 22G and 21G of the first main transformer line string in sequence, and the circuit breaker 2DL is completely isolated from the first main transformer line string; Disconnect 3DL and 32G of the second main transformer line string and 11G of the first main transformer line string, and the I bus will exit operation; disconnect 31G of the second main transformer line string, and the 3DL of the second main transformer line string will exit operation. Withdraw the circuit breaker protection of 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string; withdraw the line protection of outgoing line 1, bus protection of I bus, protection of #1 main transformer, and protection of T zone of the first main transformer line string. The DC power supply of the circuit breaker equipment corresponding to 1DL and 2DL of the first main transformer line string and 3DL of the second main transformer line string, the main transformer side bus equipment corresponding to I bus, and the line equipment corresponding to the first main transformer line string are transferred to the new DC system. Put bus I into operation, put main transformer #1 into operation, connect the 2DL and 3DL of the first main transformer line string, and put outgoing line 1 into operation; restore the circuit breaker protection of the 1DL and 2DL of the first main transformer line string and the 3DL of the second main transformer line string, and restore the protection of bus I, main transformer #1, outgoing line 1, and the T-zone protection of the first main transformer line string.

7. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to claim 4, characterized in that, Using another main transformer line maintenance window, the specific steps for de-energizing the main transformer equipment, line equipment, and circuit breaker equipment in that line, and connecting the corresponding DC load to the new DC system, include the following: Before operation, both main transformer line strings were running in full, and the protection system was operating normally. Synchronize the maintenance windows of the main transformer and the line maintenance windows of the second main transformer line string, disconnect the 2DL of the second main transformer line string, and disconnect the circuit breaker 2DL from the second main transformer line string. #2 main transformer is out of service. 1DL, 12G and 11G of the second main transformer line string are disconnected in sequence. Bus II is operating normally. Outgoing line 2 is out of service. The 3DL, 31G, 32G, 21G, and 22G lines of the second main transformer line string are disconnected in sequence. Bus I is operating normally. Exit #2 main transformer protection, outgoing line 2 line protection, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string; The DC power supply of the circuit breaker equipment corresponding to 2DL of the second main transformer line string, the main transformer equipment and line equipment corresponding to the second main transformer line string is transferred to the new DC system. Connect the 32G, 31G, and 1DL of the second main transformer line string, and put the #2 main transformer into operation; connect the 21G, 22G, and 2DL of the second main transformer line string, and put the circuit breaker into operation; put outgoing line 2 into operation; Restore the protection of main transformer #2, outgoing line 2, circuit breaker protection of the second main transformer line string 2DL, and T-zone protection of the second main transformer line string.

8. The method for retrofitting the DC system of a three-half-connection nuclear power plant switchyard according to any one of claims 1-7, characterized in that, The low-frequency disconnection panel, protection and fault information substation panel, remote communication panel, power acquisition panel, network communication panel, AVC panel, GPS time synchronization device panel, PMU host panel, and 380V switchgear control power supply DC load are classified and mapped to common equipment. Classify and map the DC loads of the main transformer bay control cabinet, the main transformer incoming line T-zone protection cabinet, and the unit interface cabinet to the main transformer equipment; Classify and map the DC loads of line protection cabinets, line bay control cabinets, and line outgoing T-zone protection cabinets to the line equipment. Classify and map the DC loads of circuit breaker protection cabinets, circuit breaker measurement and control cabinets, and circuit breaker bay control cabinets to circuit breaker equipment. The DC loads of busbar protection cabinets, busbar monitoring and control panels, and busbar bay control cabinets are classified and mapped to busbar equipment.

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