An automatic recloser is like an “automatic switch” for electrical circuits; it can automatically attempt to reclose the circuit within a few seconds after a trip, saving the need for manual intervention and reducing power outage time.
This article, written by an automatic recloser manufacturer, explains the functions and understanding of automatic reclosers, a core device in distribution network automation.
The recloser device is installed on utility poles. High-voltage lines are susceptible to lightning strikes during rainy weather, and tree branches, often taller than the lines, can come into contact with them. Therefore, a recloser device is necessary. Its function is to immediately detect abnormal current and perform tripping (opening the circuit breaker) to interrupt the fault current and protect the power grid equipment.
After tripping, the recloser waits for a preset short interval (usually 0.5-3 seconds). Falling leaves from trees don’t stay on the power lines indefinitely, so this transient fault disappears automatically as the leaves fall. Similarly, in the case of a lightning strike, the electrical arc ions in the air also have a limited duration. Therefore, the recloser device, through its components, performs a judgment process similar to human reasoning before attempting self-healing.
If the “cooling-off period” ends, the recloser will automatically attempt to reclose the circuit one or more times (usually 1-3 times). If the fault has disappeared, the line successfully restores power, and the user may only perceive a momentary voltage flicker.
The recloser device will make multiple attempts. If the fault persists after several attempts, the recloser will determine this to be a “permanent fault” (such as a broken line or equipment breakdown) and finally lock into the open circuit state. This action strictly isolates the faulty section and sends a signal to the control center, awaiting maintenance personnel to accurately locate and eliminate the fault.
Automatic reclosing devices are installed on utility poles at precisely calculated critical nodes of the power grid to be used on line segments, branch lines, or customer demarcation points.
1. Middle And End Sections Of Long-Distance Overhead Distribution Lines
Challenge: At the end of the line, far from the substation, the short-circuit current level is low, and the traditional substation outgoing circuit breaker protection lacks sensitivity. Furthermore, any fault will cause a power outage along the entire long line.
Solution: Install reclosers in the middle or at two-thirds of the line to divide the long line into several protection sections. Faults at the end of the line are isolated only by the recloser, without affecting users in the preceding sections, thus achieving precise control of the fault area.Automatic reclosers are typically installed in rural or suburban areas.
2.Important Branch Lines Or Starting Point Of Multi-User Connections
Challenge: A main line connects to multiple branches or important users; a fault in any branch can affect the entire main line.
Solution: Install a recloser (often called a “sectionalizing switch”) at the entrance of the branch line. When a branch fault occurs, the recloser trips and isolates the fault, ensuring that the main line and other branch users’ power supply remain unaffected. This is key to achieving “fault isolation without service interruption.”
Automatic reclosers are most likely to be found in distribution lines in suburban areas, towns, industrial parks, and large rural communities.
3.Remote mountainous areas, forest areas
Challenge: These areas are susceptible to lightning strikes, tree growth, and animal activity, resulting in significantly higher transient fault rates than in urban areas.
Solution: Installing reclosers as the first line of defense automatically eliminates most transient faults, preventing maintenance personnel from making frequent long-distance trips for unnecessary inspections and operations, thereby greatly improving maintenance efficiency.
4.Distributed Power Generation Grid Connection Points
Challenge: The integration of distributed power sources transforms the distribution network from a “radial” structure to a “multi-source” network, potentially altering fault current direction and complicating protection coordination.
Solution: Equip the system with voltage-time type or more advanced intelligent reclosers that can coordinate with upstream protection, prevent asynchronous closing, and reliably disconnect distributed power sources during grid faults, ensuring grid safety and the safety of maintenance personnel.
Automatic reclosers can be used in large, centralized distributed power generation facilities in rural or suburban areas, at grid-connected photovoltaic systems on factory rooftops in industrial parks, and at village-level or regional-level photovoltaic aggregation points in rural power grids.It’s not just a switch, but a “manager” with the ability to make judgments.
5.Critical Power Supply Network Nodes In The City
Challenge: To improve the reliability of power supply in the city center, a “hand-in-hand” ring network connection is often used. In case of a fault, it is necessary to quickly locate and isolate the fault and transfer the load.
Solution: Reclosers (often circuit breaker type) are installed at the ring network substations. Combined with a communication network, this allows for fault section isolation and power restoration to the non-faulty sections within milliseconds, achieving “self-healing power supply.”
Automatic reclosers can be found on sidewalks or green belts along roads, inside large industrial parks, near subway stations, and within plots of land in the city’s core area.
It is necessary to match the maximum operating voltage and long-term load current of the system, and consider the margin for future load growth.
PS: Pay attention to whether the insulation level (such as lightning impulse withstand voltage) meets local environmental requirements.
It should be greater than the maximum expected short-circuit current at the installation site, and the transient recovery voltage (TRV) withstand capacity should be verified.
The duration of withstanding short-circuit current (such as 1s or 3s) must meet the stability requirements of the system.
The number of full capacity disconnections and mechanical operations (such as more than 10000 times) affects the long-term reliability of the equipment.
Recloser Fault Type Detection: Transient VS Permanent
Automatic recloser is based on a preset ‘action sequence’. The automatic recloser is judged by the preset upper limit of automatic reclosing times: if the reclosing is successful within the number of times, it is judged as an instantaneous fault; if it still fails after exceeding the number of times, it is judged as a permanent fault and ultimately locked.
Automatic Recloser VSOrdinary Circuit Breaker VS Fuse
The main difference lies in intelligence and the ability to repeat actions. Ordinary circuit breakers (requiring manual or remote reset) and fuses (requiring manual replacement) stop working immediately after tripping or melting.
The recloser integrates a control unit and can automatically and repeatedly attempt to restore power supply, making it an active “”self-healing”” device. It is often used in conjunction with fuses to achieve selective coordination of upper and lower level protection.
How to Select the Right Auto Recloser
Selecting the appropriate automatic recloser requires careful evaluation of: electrical parameters, control and intelligence, environmental and mechanical factors, and integration and cost.
Benefits of Auto Reclosers in Power Distribution
Using automatic reclosers in power distribution networks can improve reliability, enhance operational efficiency, facilitate fault isolation, and serve as a foundation for smart grids.
circuit breaker VS auto recloser
The core difference lies in their core functions and level of intelligence.
Circuit breakers are used to interrupt fault currents and then wait for manual or remote commands to reclose.
Automatic reclosers combine protection functions with autonomous learning capabilities, allowing for multiple timed reclosing attempts after a trip. If the fault is temporary, power can be automatically restored.
Automatic reclosers are used for rapid fault isolation, fault self-healing assessment, automatic power restoration attempts, and permanent fault lockout.
Automatic reclosers are installed in the middle sections of long-distance overhead distribution lines, at the starting points of important branch lines or multi-user connections, in remote mountainous areas, forest areas, and at distributed power generation grid connection points and critical power supply network nodes in the city.
Want to learn more about reclosers in distribution network equipment? Stay tuned for future articles as we continue to analyze the intelligent pulse of the power grid.
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