What is Automatic Circuit Recloser: Principle, Types, and Functions

An Automatic Circuit Recloser (ACR), sometimes referred to as an automatic line recloser, is an effective fault automation technology widely applied in power lines. When a power line experiences a fault, after the protective relaying system trips the circuit breaker to clear the fault, the automatic circuit recloser device will automatically reclose it after a short time interval.

Experience in power system operation shows that the vast majority of overhead line faults (over 80-90%) are transient faults. These faults are typically caused by lightning strikes, wind damage, tree branch contact, bird interference, or insulator flashovers. When the protective relay operates to clear a short-circuit fault, the fault point de-ionizes automatically, the arc extinguishes, and the line’s insulation can quickly recover. At this point, the automatic circuit recloser recloses the circuit breaker, enabling timely restoration of line operation and significantly enhancing the reliability of the power supply.

Only a small percentage (usually less than 10%) are permanent faults (e.g., downed poles, broken lines, insulator breakdown damage). In such cases, if the auto recloser attempts to reclose and the fault persists, the protective relay will trip the circuit breaker again, stopping power supply. The cause must then be investigated and rectified.

How does A Recloser Work?

The auto recloser working principle is based on its intelligent management and restoration capabilities within power lines. Its core lies in cleverly utilizing the transient nature of power line faults. When a line experiences a transient fault (e.g., due to a lightning strike or foreign objects blown by wind), the protective relaying system immediately issues a command to quickly cut off power, causing the circuit breaker to trip and isolate the fault.

At this point, the recloser waits patiently for a very short “dead time” (typically 0.15-0.5 seconds). This interval is sufficient for the arc at the fault point to extinguish, ionized particles in the air to dissipate, and the line’s insulation performance to naturally recover.

After the waiting period, the recloser controller (such as Liyond’s BC300/BC500 series) issues another command to attempt to automatically close the circuit breaker, restoring power to the line. If the line successfully recovers, it means the fault was indeed transient, and power supply is quickly restored without manual intervention, significantly reducing outage time and losses.

However, if the fault is permanent (e.g., a fallen pole, broken line), the recloser’s first attempt will fail, and the protective relay will trip again. In this scenario, the recloser device enters a “lockout” state, discontinuing further reclosing attempts and awaiting maintenance personnel intervention. This intelligent mechanism effectively distinguishes between transient and permanent faults, avoiding repeated stress on equipment due to persistent faults while maximizing power supply continuity.

Key Functions of Auto Reclosers in Power Systems

An automatic circuit recloser device is not merely an effective means of restoring power; it plays several vital roles in power systems:

Significantly Improves Power Supply Reliability and Reduces Outage Losses: This is its primary function. Since most line faults are transient, the autorecloser can quickly restore power, preventing significant losses to the economy and users from prolonged outages, especially for single-fed radial lines.

Enhances Power System Transient Stability: The use of automatic circuit reclosers on high-voltage transmission lines can reduce system oscillations caused by short-circuit faults, thereby improving the stability of parallel operation and the transmission capacity of the lines.

Saves Grid Construction Investment: In power grid design and construction, considering the role of the recloser can, in certain situations, defer the need to build double-circuit lines, thus saving substantial investment.

Corrects False Trips: An automatic circuit recloser can also correct false trips caused by faulty circuit breaker mechanisms or protective relay malfunctions, further ensuring power supply continuity.

Ensures Industrial Production: For critical industrial equipment that would lead to plant shutdown if power is lost (such as boiler feed pumps, fuel pumps, or fans), the auto recloser ensures rapid power restoration after temporary faults, preventing disruptions to normal production and enhancing operational safety and reliability.

Recloser Types and Selection

Based on power system structure, operational requirements, and voltage levels, various recloser types and configurations exist:

Recloser Types by Number of Phases

Three-Phase Single-Shot Recloser: Most 3 phase recloser devices adopt this type, where all three phases operate simultaneously and reclose once.

Three-Phase Multiple-Shot Recloser: Used in a minority of cases, allowing the three phase recloser to reclose more than once.

Single-Phase Autorecloser: Primarily used for high-voltage long-distance transmission lines, where faults cause single-phase tripping followed by single-phase reclosing, which helps maintain system stability.

Comprehensive Recloser: For single-phase faults, single-phase tripping and reclosing occur; for multi-phase faults, three-phase tripping occurs, followed by three-phase reclosing. This is a more flexible autorecloser method.

Recloser Classification by Power Source Configuration

Single-Source Feeder Lines: Typically only require a standard three-phase single-shot recloser.

Dual-Source Feeder Lines: Require synchronous check reclosers to address synchronization issues between the two power sources (i.e., no-voltage verification and synchronization verification), ensuring safe closing.

Recloser Types by Number of Operations

Single-Shot Recloser: This method is primarily adopted in many power systems, allowing only one reclosing attempt.

Multiple-Shot Recloser: May be applied in certain specific operational scenarios.

The success rate of automatic circuit reclosers is influenced by various factors such as voltage level, line structure, main fault types, and weather conditions. According to relevant industry statistics, the success rate generally ranges from 60% to 90%.

Basic Requirements for Recloser Devices

To ensure the safe and reliable operation of an automatic circuit recloser device, the following basic requirements must be met:

Prohibition of Reclosing Conditions:

When the circuit breaker is tripped manually by operation personnel or via remote control, the recloser should not operate.

If a permanent fault exists on the line after a manual closing operation, causing immediate tripping by protection, the recloser should not operate.

Mandatory Reclosing Conditions:

Except for the two situations above, when a circuit breaker trips due to protective relay operation or other reasons, the recloser should operate to reclose the vacuum circuit breaker under satisfied conditions.

Operation Count Limit:

The number of operations of the autorecloser device must strictly adhere to predefined settings; for example, a single-shot recloser should only reclose once and not allow a second reclose.

Automatic Reset:

After completing its operation, the automatic circuit recloser should generally reset automatically, preparing for subsequent potential faults and reclosing operations.

Coordination with Protective Relays:

It should coordinate with protective relays to achieve accelerated or delayed fault clearance, optimizing fault clearing time. When closing with a control switch, measures to accelerate protective relay operation should be adopted.

Synchronization Issue Handling:

When reclosers are implemented on dual-source feeder lines, synchronization issues between the two power sources must be considered, requiring no-voltage verification and synchronization verification functions.

Lockout Function:

When the circuit breaker is in an abnormal state (e.g., low gas pressure or oil pressure) and reclosing is not permitted, the automatic circuit recloser device should automatically lockout to prevent unsafe operation.

Starting Principle:

The automatic circuit recloser should ideally be initiated based on the principle of a mismatch between the control switch position and the circuit breaker position to enhance power supply reliability and system operational stability, and to correct circuit breaker misoperations or “ghost trips.”

Recloser Starting Methods

An automatic circuit recloser device primarily has two starting methods, each with its characteristics:

Control Switch Position vs. Circuit Breaker Position Mismatch Starting Method:

Advantages: This method is simple, reliable, and forms the basic starting principle for all reclosers. It can also correct circuit breaker misoperations or unexpected trips, effectively improving power supply reliability and system operational stability. It demonstrates good operational performance across various grid levels.

Disadvantages: This starting method might fail if the auxiliary contact switch of circuit breaker is faulty.

Protection-Initiated Starting Method:

Advantages: This method is an important complement to the mismatch starting method. In the process of single-phase reclosing, to achieve certain protection lockouts and select/fix the fault phase in the logic circuit, a recloser starting element initiated by protection is required.

Disadvantages: The protection-initiated starting method cannot correct false trips caused by faulty circuit breaker mechanisms or misoperations.

Both starting methods usually work in conjunction to collectively ensure the reliable operation of the automatic circuit recloser device.

Liyond Automatic Circuit Recloser Solutions

As a leading auto recloser manufacturer in power automation, Liyond offers a range of high-performance automatic circuit recloser products designed to meet the stringent requirements of various voltage levels and application scenarios from distribution to transmission. Our product line includes 15kV outdoor recloser, 27kV outdoor auto recloser, and 38kV recloser, all compatible with advanced recloser controller units to provide reliable and intelligent fault management solutions for global power systems.

Liyond’s autorecloser products ensure power supply continuity and system stability with their excellent design and technical characteristics:

Robust and Durable Construction: For instance, the LYVZ15 15kV recloser features a one-piece epoxy resin body, providing excellent insulation and hydrophobicity for all-weather reliability. The LYVZ27 27kv recloser uses a unibody epoxy resin housing and a powder-coated stainless steel tank, offering outstanding insulation and corrosion resistance in polluted or humid environments. Our general outdoor recloser models also feature robust powder-coated stainless steel tanks protecting internal mechanisms, with external mechanical indicators providing instant status visibility.

Precise and Efficient Operation: Our products generally employ high-capacity magnetic actuators to achieve synchronized three-phase tripping and closing, ensuring operational precision and reliability.

Intelligent Control and Communication: The accompanying microprocessor-based recloser controller (such as BC300/BC500) provides a comprehensive solution integrating protection, control, monitoring, metering, and data logging. It supports multiple programmable reclose cycles (up to 4 reclose/5 trip operations) and customizable protection schemes, including various phase overcurrent protection, ground overcurrent protection, negative sequence overcurrent protection, directional overcurrent protection, over-frequency protection, and over/under voltage alarms. Through RS485/RS232 ports, seamless integration with SCADA systems and remote diagnostics and control are achievable.

Safe and Convenient Operation: All models prioritize operational safety. For example, the LYVZ27 outdoor recloser supports safe hot stick operation to the open position via an accessible yellow pull ring for easy maintenance. Our general three phase recloser also supports manual operation via hot stick and a pull ring mechanism, ensuring safety during maintenance.

Choosing Liyond recloser solutions means opting for industry-leading technology, reliable performance, and comprehensive service support, empowering your grid to move towards a smarter, more reliable future. For more product details or customized solutions, please feel free to contact us.

Conclusion

In summary, the automatic circuit recloser is an indispensable automation device in modern power systems. By intelligently identifying and clearing transient line faults, it significantly enhances power supply reliability, stability, and economic efficiency. From its definition to its working principle, from its diverse types to its stringent basic requirements, and its various starting methods, the autorecloser plays a core role in ensuring the safe and efficient operation of power systems. Liyond, as a dedicated recloser manufacturer, is committed to providing high-performance, intelligent, and reliable automatic circuit recloser products, meeting the demanding needs of current and future grids. As smart grids continue to develop, recloser technology will also evolve, contributing to the construction of more resilient power infrastructure.