A method for locating and isolating inter-pole short-circuit faults in low-voltage DC distribution networks

Abstract

This invention belongs to the field of power system relay protection technology and discloses a method for locating and isolating inter-pole short-circuit faults in low-voltage DC distribution networks. The method includes: acquiring the current amplitude and direction flowing through each boundary switch of the same protection zone, the data being monitored in real time by the protection device at the corresponding switch; establishing a communication connection between the protection devices at each boundary switch of the same protection zone to exchange data in real time; performing a composite fault determination based on a combined criterion of current amplitude difference threshold and direction deviation; if the monitored currents are equal in magnitude and direction, the zone is fault-free; if the current difference reaches a threshold or the directions are opposite, a short-circuit fault is determined to exist in the protection zone; finally, controlling the corresponding switch to trip according to the specific electrical circuit type. This invention effectively eliminates monitoring blind spots, achieves millisecond-level precise location and collaborative isolation, significantly reduces reliance on expensive DC solid-state circuit breakers, and balances speed, selectivity, and economy.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, specifically to a method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network. Background Technology

[0002] Low-voltage direct current (DC) distribution technology, with its significant advantages such as low line loss, high power supply reliability, and easy compatibility with distributed power sources, has enormous application potential in smart grids and "photovoltaic-storage-DC-flexible" systems. However, protection technology for DC systems remains a key bottleneck restricting its development. In DC systems, when an inter-pole short-circuit fault occurs, the fault current rises extremely rapidly and has no natural zero-crossing point, making arc extinguishing by circuit breakers extremely difficult, thus placing extremely high demands on the speed of protection devices. Currently, while DC solid-state circuit breakers are fast, they are expensive and have limited capacity, while alternative solutions such as fast-acting fuses have significant shortcomings in selective coordination.

[0003] In terms of fault detection, traditional protection methods based on current amplitude struggle to accurately distinguish fault current differences in low-impedance DC lines, easily leading to maloperation or failure of protection devices. Furthermore, due to the low overcurrent withstand capability of voltage source converters, the protection system must complete fault detection and isolation within an extremely short time.

[0004] Currently, there is a lack of cost-effective networked solutions for the coordinated protection of low-voltage switchgear and distribution boxes. Existing methods often fail to achieve a good balance between reliability, speed, selectivity, and economy. Therefore, there is an urgent need to research new networked protection principles that can achieve precise fault location and rapid isolation through information interaction and coordinated control between intelligent terminals, thereby ensuring the safe and stable operation of the system. Summary of the Invention

[0005] To address the technical problems of existing low-voltage DC distribution networks where inter-pole short-circuit faults result in rapid rise and unclear characteristics of the fault current, making it difficult for traditional protection methods to balance speed and selectivity, and leading to high system construction costs due to over-reliance on expensive DC solid-state circuit breakers, this invention designs a method for locating and isolating inter-pole short-circuit faults in low-voltage DC distribution networks. The specific technical solution is as follows: A method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network includes the following steps: S1: Obtain the current amplitude and current direction of each boundary switch in the same protection area of ​​the DC power distribution circuit. The current amplitude and current direction are obtained in real time by the protection device at the corresponding boundary switch. A communication connection is established between the protection devices at each boundary switch in the same protection area to exchange the data of the current amplitude and current direction in real time. S2: Based on the current amplitude and current direction monitored in real time by the protection devices at each boundary switch of the same protection area, perform composite fault determination, and locate the area where the inter-pole short circuit fault is located based on the composite fault determination result. S3: When it is determined that there is an inter-pole short circuit fault in the protection area, the corresponding communication protection logic is adopted according to the specific electrical circuit type involved in the protection area to control the switch corresponding to the fault area with the inter-pole short circuit fault to perform a tripping action.

[0006] In a preferred implementation, the topology of the DC distribution network includes a DC cabinet, which has segmented busbars inside. The incoming line powered by the main power supply is connected to the busbar through its corresponding incoming line switch. Different segments of the busbar are connected to each other through a bus tie circuit with a bus tie switch. The feeder supplying power to the next level distribution area is connected to the busbar through its corresponding feeder switch.

[0007] In a preferred implementation, a communication connection is established between the protection devices at the boundary switches of the same protection area to exchange data on the current amplitude and the current direction in real time, specifically including: A synchronous sampling mechanism is used to obtain the current sampling data and corresponding timestamps of the protection devices at each boundary switch of the same protection area, so as to ensure the consistency of the timing of real-time interactive data. In the transmission of real-time interactive data, perform automatic removal of abnormal data and verification and retransmission operations.

[0008] In a preferred implementation, the step of performing composite fault determination based on the current amplitude and current direction monitored in real time by the protection devices at each boundary switch of the same protection area specifically includes: A dynamic adaptive threshold value is set based on the combined criterion of the difference threshold of the current amplitude and the direction deviation. If the current amplitude and direction of the current monitored in real time at the protection devices at each boundary switch of the same protection area are equal, it is determined that there is no inter-pole short circuit fault in the current protection area. If the difference in current amplitude monitored in real time by the protection devices at the boundary switches of the same protection area reaches the dynamic adaptive threshold or the current direction is opposite, it is determined that there is an inter-pole short circuit fault in the current protection area.

[0009] In a preferred implementation, if the protection area involves the incoming line and bus tie circuit of the DC cabinet, then the corresponding communication protection logic is a first communication protection logic, specifically including: Based on real-time communication, the direction of the short-circuit current at the bus tie switch is obtained, and it is determined whether the inter-pole short-circuit fault point is located in the bus section or in the downstream feeder circuit connected to the bus section. When the inter-pole short-circuit fault is located in the downstream feeder circuit, if the fault current is cut off by the feeder switch corresponding to the downstream feeder circuit within a set time threshold, the incoming switch and the bus tie switch are controlled to remain inactive; if the fault current still exists after the time threshold is exceeded, the incoming switch is controlled to perform a tripping action.

[0010] In a preferred implementation, if the protection area involves the incoming and feeding lines of the DC cabinet, the corresponding communication protection logic is a second communication protection logic, specifically including: If a fault current is detected in the feeder of the DC cabinet in real time, the incoming line switch and the bus tie switch will be kept inactive.

[0011] In a preferred implementation, the DC distribution network further includes a primary distribution box located one level below the DC cabinet, the primary distribution box being provided with a distribution box inlet line and a corresponding distribution box inlet line switch; In a radial power distribution network topology, if the protection zone involves the feeder of a DC cabinet and the incoming line of a primary distribution box, then the corresponding communication protection logic is the third communication protection logic, specifically including: If there is a fault current in both the feeder of the DC cabinet and the incoming line of the primary distribution box, and the fault currents at both locations are in the same direction and the difference in current amplitude is less than a set threshold, then the feeder switch of the DC cabinet will be kept inactive. If there is a fault current in the feeder of the DC cabinet and there is no current in the incoming line of the primary distribution box, the feeder switch of the DC cabinet shall be controlled to trip.

[0012] In a preferred implementation, under a ring network topology, if the protection zone involves the feeder of a DC cabinet and the incoming line of a primary distribution box, then the corresponding communication protection logic is a fourth communication protection logic, specifically including: If there is a fault current in both the feeder of the DC cabinet and the incoming line of the primary distribution box, and the fault currents at both locations are in the same direction and the difference in current amplitude is less than a set threshold, the DC cabinet feeder switch is controlled to remain inactive. If there is a fault current in the feeder of the DC cabinet, and there is no current or a reverse fault current in the incoming line of the primary distribution box, the DC cabinet feeder switch and the primary distribution box incoming line switch will both trip.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention requires the protection devices at the boundary switches of the same protection area to establish a communication connection. Through the composite criteria of current direction and magnitude, it can respond to the changes in electrical quantity in the early stage of the fault very quickly, realize the fault perception and accurate location in milliseconds, and solve the technical defects of traditional current protection in low impedance DC lines, which makes it difficult to distinguish fault current and easily leads to false tripping or failure to trip.

[0014] (2) By using precise fault location and collaborative isolation strategies, this invention reduces the requirement for accurate and rapid identification of fault current by low-voltage DC circuit breakers. The system is allowed to use mechanical DC circuit breakers with lower breaking time and lower cost, thereby getting rid of the excessive reliance on expensive and limited-capacity DC solid circuit breakers and significantly reducing the hardware cost of the entire protection system.

[0015] (3) The various communication protection logics designed in this method are not only applicable to DC cabinet bus protection and conventional radial distribution networks, but also have great potential for application in ring network distribution topologies with bidirectional current flow. Through information interaction between intelligent terminals, the problem of collaborative protection under complex networks is solved.

[0016] (4) In the event of a short circuit, the present invention only issues a trip command to the switch in the faulty section that is determined to be an inter-pole short circuit, thereby achieving precise fault isolation. This method effectively prevents cascading tripping, enabling non-faulty sections to quickly restore normal power supply after a brief disturbance, thus strongly ensuring the safe and stable operation of the DC distribution network. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a flowchart illustrating the method for locating and isolating inter-pole short-circuit faults in low-voltage DC distribution networks according to the present invention.

[0019] Figure 2 This is a schematic diagram of a typical circuit fault point in the low-voltage DC distribution network of the present invention.

[0020] Figure 3 This is a schematic diagram of the first communication protection logic in this invention.

[0021] Figure 4 This is a schematic diagram of the second communication protection logic in this invention.

[0022] Figure 5 This is a schematic diagram of the third communication protection logic in this invention.

[0023] Figure 6 This is a schematic diagram of the fourth communication protection logic in this invention.

[0024] Figure 7This refers to the direction of the short-circuit current under the short-circuit fault condition (K1) of the DC cabinet bus in this invention.

[0025] Figure 8 This refers to the direction of the short-circuit current under the fault condition (K2) of the radial power distribution feeder in this invention.

[0026] Figure 9 This refers to the direction of the short-circuit current under the fault condition (K3) of the last-stage feeder circuit in the distribution box in this invention.

[0027] Figure 10 This refers to the direction of the short-circuit current under fault condition (K4) of the primary feeder circuit of the radial distribution box in this invention.

[0028] Figure 11 This refers to the direction of the short-circuit current under the fault condition (K5) of the ring network distribution feeder in this invention.

[0029] Figure 12 This refers to the direction of the short-circuit current under the fault condition (K6) between the ring network distribution boxes in this invention.

[0030] Figure 13 The direction of the short-circuit current under the fault condition (K7) of the ring network distribution box in this invention.

[0031] Figure 14 The direction of the short-circuit current under the fault condition (K8) of the primary feeder of the ring network distribution box in this invention. Detailed Implementation

[0032] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0034] Example 1: A General Method for Locating and Isolating Inter-Pole Short-Circuit Faults in Low-Voltage DC Distribution Networks See Figure 1 This invention provides a method for locating and isolating inter-pole short-circuit faults in low-voltage DC distribution networks, applicable to, for example... Figure 1 The typical circuit of the low-voltage DC power distribution system shown includes the following steps: S1: Obtain the current amplitude and current direction of each boundary switch in the same protection area of ​​the DC power distribution circuit. The current amplitude and current direction are obtained in real time by the protection device at the corresponding boundary switch. The protection devices at each boundary switch in the same protection area establish a communication connection to exchange the data of the current amplitude and current direction in real time.

[0035] Specifically, a synchronous sampling mechanism is used to obtain the current sampling data and corresponding timestamps of the protection devices at each boundary switch of the same protection area, and abnormal data is automatically removed and verified and retransmitted during the data transmission of real-time interactive data.

[0036] S2: Based on the current amplitude and current direction monitored in real time by the protection devices at each boundary switch of the same protection area, perform composite fault determination, and locate the area where the inter-pole short circuit fault is located based on the composite fault determination result. Specifically, a dynamic adaptive threshold value is set based on a combined criterion of current amplitude difference threshold and direction deviation to cope with fault conditions. If the current magnitudes and directions monitored in real time by the protection devices at each boundary switch of the same protection zone are equal, it is determined that there is no inter-pole short circuit fault in the zone; if the current differences are large or the directions are opposite, it is determined that there is an inter-pole short circuit fault in the zone.

[0037] S3: When it is determined that there is an inter-pole short circuit fault in the protection area, the corresponding communication protection logic is adopted according to the specific electrical circuit type involved in the protection area to control the switch corresponding to the fault area with the inter-pole short circuit fault to perform tripping action, thereby achieving fault isolation and enabling the non-faulty section to quickly restore normal power supply after a brief disturbance.

[0038] Example 2: Communication Protection Logic and Operating Condition Application Based on DC Cabinet Level This embodiment combines Figure 2 The illustrated topology details the communication protection logic within the DC cabinet and at the outgoing terminals. The DC distribution network topology includes a DC cabinet, which contains segmented busbars. Incoming lines powered by the mains supply pass through their corresponding incoming line switches (e.g., ...). Figure 2 CB01 and CB02 are connected to the busbar, and different sections of the busbar are connected by a bus tie switch ( Figure 2 The feeder is connected to the bus tie circuit of CB03 in the middle, and the feeder supplying power to the next level of power distribution area is connected through its corresponding feeder switch (such as CB03 in the middle). Figure 2 CB11, CB12, and CB13 are connected to the busbar.

[0039] For this topology, this invention designs handling mechanisms for eight typical inter-pole short-circuit fault conditions (K1-K8). Specifically, K1-K8 are: DC cabinet bus inter-pole short-circuit fault condition, radial distribution feeder fault condition, last-stage feeder circuit fault condition of distribution box, first-stage feeder circuit fault condition of radial distribution box, ring network distribution feeder fault condition, line fault condition between ring network distribution boxes, busbar fault condition of ring network distribution box, and first-stage feeder fault condition of ring network distribution box.

[0040] refer to Figure 3 In this embodiment, the present invention discloses a first communication protection logic, specifically addressing the DC cabinet busbar inter-pole short-circuit fault condition (K1): if the protection area involves the DC cabinet's incoming line and bus tie circuit, by determining the direction of the short-circuit current at the bus tie, it is determined that the inter-pole short-circuit fault point is located in the busbar section or in the downstream feeder circuit connected to the busbar section. For example... Figure 7 As shown, when a short-circuit fault occurs between poles of the DC cabinet bus (K1), the system detects the fault current and activates the communication protection of CB01, CB02, and CB03. By identifying the direction of the short-circuit current at the bus tie switch CB03, the system controls the incoming line switch CB01 and the bus tie switch CB03 to trip. Simultaneously, the reverse current protection of the feeder switch CB12 is activated. Since a reverse current is detected in CB12, the system controls CB12 to trip, thereby clearing the fault.

[0041] refer to Figure 4 In this embodiment, the present invention discloses a second communication protection logic, specifically addressing the radial distribution feeder fault condition (K2): if the protection area involves the incoming line and feeder of the DC cabinet, when real-time communication detects a fault current in the feeder, the incoming line switch and bus tie switch are controlled to remain inactive. Figure 8 As shown, when a radial distribution feeder fault occurs (K2), the system detects the fault current and activates the communication protection between the DC cabinet incoming line CB01 and feeder CB11. Because a fault current is detected in feeder CB11, the system controls the upstream switch CB11 to trip. Simultaneously, the system controls incoming switches CB01 and CB02 and the bus tie switch CB03 to remain inactive, achieving cross-level isolation.

[0042] Example 3: Communication Protection Logic and Operating Condition Application in Radial Power Distribution Networks This embodiment combines Figure 2 This paper elucidates the collaborative logic of distribution boxes at each level in a radial network. The DC distribution network also includes primary distribution boxes located one level below the DC cabinet, equipped with distribution box incoming lines and corresponding incoming line switches (such as CB21, CB31, CB32).

[0043] refer to Figure 5In this embodiment, the present invention discloses a third communication protection logic, specifically addressing the fault conditions (K3) of the final feeder circuit of the distribution box and the fault conditions (K4) of the primary feeder circuit of the radial distribution box: In the radial topology, if there is a fault current in both the DC cabinet feeder and the primary distribution box incoming line, and the fault current directions at both locations are the same and the difference in current amplitude is less than a set threshold, then the DC cabinet feeder switch is controlled to remain inactive; if there is a fault current in the DC cabinet feeder and there is no current in the distribution box incoming line, then the DC cabinet feeder switch is controlled to trip.

[0044] In the application scenario of fault condition (K3) of the last-stage feeder circuit in the distribution box, such as Figure 9 As shown, when a fault occurs in the last-level feeder circuit of the distribution box (K3), the short-circuit instantaneous protection set by the inverter (chopper) itself is activated at the bottom layer, directly cutting off the fault current.

[0045] In the application scenario of fault condition (K4) of the primary feeder circuit of the radial distribution box: such as Figure 10 As shown, when a fault occurs in the primary feeder circuit of the radial distribution box (K4), the communication protection of CB11 and CB21 is activated. Because there are fault currents with the same direction and current amplitude differences less than the set threshold, CB11 and CB21 are kept inactive. The bottom-level switch CB32 instantaneously trips to clear the fault; if CB32 fails to trip, CB21 trips with a short delay (e.g., 30ms) as a backup.

[0046] Example 4: Communication Protection Logic and Operating Condition Application in Ring Network Power Distribution This embodiment describes a complex ring network topology, referencing... Figure 6 This embodiment discloses a fourth communication protection logic, specifically addressing the following conditions: ring network distribution feeder fault (K5), ring network distribution box line fault (K6), ring network distribution box busbar fault (K7), and ring network distribution box primary feeder fault (K8). If both the DC cabinet feeder and the primary distribution box incoming line have fault current, and the fault current directions at both locations are the same and the current amplitude difference is less than a set threshold, the DC cabinet feeder switch is controlled to remain inactive. If there is fault current and there is no current in the distribution box incoming line or there is a reverse fault current, the DC cabinet feeder switch and the primary distribution box incoming line switch are controlled to trip.

[0047] In the application scenario of ring network distribution feeder fault condition (K5), such as Figure 11As shown: When a ring network distribution feeder fault occurs (K5), CB12 and CB22 activate communication protection, determine that the fault currents of the upstream and downstream lines are in opposite directions (CB12 has a forward fault current, and CB22 has a reverse backflow current), and control CB12 and CB22 to simultaneously trip to clear the fault. Meanwhile, CB13 and CB25 of the other branch have fault currents in the same direction, and control them to remain inactive.

[0048] In the application scenario of line fault condition (K6) between ring network distribution boxes, such as Figure 12 As shown: When a line fault occurs between the ring network distribution boxes (K6), CB24 and CB23 activate differential protection. They determine that the directions of the fault currents at the two locations are opposite, thus meeting the differential protection conditions, and control CB24 and CB23 to perform tripping actions.

[0049] In application scenarios such as busbar fault condition (K7) or primary feeder fault condition (K8) of ring network distribution box, such as Figure 13 and Figure 14 As shown, when a busbar fault occurs in the ring network distribution box (K7) or a primary feeder fault occurs in the ring network distribution box (K8), the system determines through communication protection IV that the upstream nodes (such as CB12, CB22, or CB13, CB25) are all experiencing unidirectional through-fault currents, and then controls the corresponding switches to remain inactive. The fault is ultimately precisely cleared by the short-delay protection of CB22 and CB23 (for K7), or by the instantaneous protection of CB33 and the backup protection of CB22 and CB23 (for K8).

[0050] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network, characterized in that, Includes the following steps: S1: Obtain the current amplitude and current direction of each boundary switch in the same protection area of ​​the DC power distribution circuit. The current amplitude and current direction are obtained in real time by the protection device at the corresponding boundary switch. A communication connection is established between the protection devices at each boundary switch in the same protection area to exchange the data of the current amplitude and current direction in real time. S2: Based on the current amplitude and current direction monitored in real time by the protection devices at each boundary switch of the same protection area, perform composite fault determination, and locate the area where the inter-pole short circuit fault is located based on the composite fault determination result. S3: When it is determined that there is an inter-pole short circuit fault in the protection area, the corresponding communication protection logic is adopted according to the specific electrical circuit type involved in the protection area to control the switch corresponding to the fault area with the inter-pole short circuit fault to perform a tripping action.

2. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 1, characterized in that, The topology of the DC distribution network includes a DC cabinet, which has segmented busbars inside. The incoming line powered by the main power supply is connected to the busbar through its corresponding incoming line switch. Different segments of the busbar are connected to each other through a bus tie circuit with a bus tie switch. The feeder supplying power to the next level distribution area is connected to the busbar through its corresponding feeder switch.

3. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 1, characterized in that, A communication connection is established between the protection devices at each boundary switch of the same protection area to exchange data on the current amplitude and current direction in real time, specifically including: A synchronous sampling mechanism is used to obtain the current sampling data and corresponding timestamps of the protection devices at each boundary switch of the same protection area, so as to ensure the consistency of the timing of real-time interactive data. In the transmission of real-time interactive data, perform automatic removal of abnormal data and verification and retransmission operations.

4. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 1, characterized in that, The method of determining a composite fault based on the real-time monitoring of the current amplitude and direction by the protection devices at each boundary switch of the same protection zone specifically includes: A dynamic adaptive threshold value is set based on the combined criterion of the difference threshold of the current amplitude and the direction deviation. If the current amplitude and direction of the current monitored in real time at the protection devices at each boundary switch of the same protection area are equal, it is determined that there is no inter-pole short circuit fault in the current protection area. If the difference in current amplitude monitored in real time by the protection devices at the boundary switches of the same protection area reaches the dynamic adaptive threshold or the current direction is opposite, it is determined that there is an inter-pole short circuit fault in the current protection area.

5. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 2, characterized in that, If the protection area involves the incoming line and bus tie circuit of the DC cabinet, then the corresponding communication protection logic is the first communication protection logic, specifically including: Based on real-time communication, the direction of the short-circuit current at the bus tie switch is obtained, and it is determined whether the inter-pole short-circuit fault point is located in the bus section or in the downstream feeder circuit connected to the bus section. When the inter-pole short-circuit fault is located in the downstream feeder circuit, if the fault current is cut off by the feeder switch corresponding to the downstream feeder circuit within a set time threshold, the incoming switch and the bus tie switch are controlled to remain inactive; if the fault current still exists after the time threshold is exceeded, the incoming switch is controlled to perform a tripping action.

6. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 2, characterized in that, If the protection area involves the incoming and feeding lines of the DC cabinet, then the corresponding communication protection logic is the second communication protection logic, specifically including: If a fault current is detected in the feeder of the DC cabinet in real time, the incoming line switch and the bus tie switch will be kept inactive.

7. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 2, characterized in that, The DC distribution network also includes a primary distribution box located one level below the DC cabinet. The primary distribution box is equipped with a distribution box inlet line and a corresponding distribution box inlet line switch. In a radial power distribution network topology, if the protection zone involves the feeder of a DC cabinet and the incoming line of a primary distribution box, then the corresponding communication protection logic is the third communication protection logic, specifically including: If there is a fault current in both the feeder of the DC cabinet and the incoming line of the primary distribution box, and the fault currents at both locations are in the same direction and the difference in current amplitude is less than a set threshold, then the feeder switch of the DC cabinet will be kept inactive. If there is a fault current in the feeder of the DC cabinet and there is no current in the incoming line of the primary distribution box, the feeder switch of the DC cabinet shall be controlled to trip.

8. The method for locating and isolating inter-pole short-circuit faults in a low-voltage DC distribution network according to claim 7, characterized in that, In a ring network topology, if the protection zone involves the feeder of a DC cabinet and the incoming line of a primary distribution box, the corresponding communication protection logic is the fourth communication protection logic, which specifically includes: If there is a fault current in both the feeder of the DC cabinet and the incoming line of the primary distribution box, and the fault currents at both locations are in the same direction and the difference in current amplitude is less than a set threshold, the DC cabinet feeder switch is controlled to remain inactive. If there is a fault current in the feeder of the DC cabinet, and there is no current or a reverse fault current in the incoming line of the primary distribution box, the DC cabinet feeder switch and the primary distribution box incoming line switch will both trip.

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