Automatic Reclosing Modes: Single, Three-Phase & Composite

General Overview of Automatic Reclosing Modes

Typically, automatic reclosing devices are categorized into four modes: single-phase reclosing, three-phase reclosing, composite reclosing, and disabled reclosing. The appropriate mode can be selected based on load requirements and system conditions.

1. Single-Phase Reclosing

Most 110kV and higher transmission lines employ three-phase single-shot reclosing. According to operational experience, over 70% of short-circuit faults in high-voltage overhead lines within solidly grounded systems (110kV and above) are single-phase-to-ground faults. For 220kV and higher lines, due to larger phase spacing, single-phase ground faults can account for up to 90% of all faults. In such cases, disconnecting only the faulty phase and performing single-phase reclosing—while keeping the two healthy phases energized during the reclosing cycle—significantly improves power supply reliability and enhances the stability of parallel system operation. Therefore, single-phase reclosing is widely used in solidly grounded systems of 220kV and above.

It is generally applied to:

• 220kV and below single-circuit tie lines;

• Lines with weak interconnection between two power sources (including electromagnetic loop networks weakly connected via lower-voltage lines);

• High-voltage outgoing lines from large steam turbine generator units.

2. Composite Reclosing

Composite reclosing applies single-phase reclosing for single-phase-to-ground faults and three-phase reclosing for phase-to-phase faults.

It is typically used on lines where three-phase reclosing is permitted, but single-phase reclosing offers better performance in maintaining system stability or restoring power supply.

3. Three-Phase Reclosing

Three-phase reclosing refers to a method where, regardless of whether a single-phase or phase-to-phase fault occurs on transmission or distribution lines, the protective relay trips all three phases of the circuit breaker simultaneously, followed by the automatic reclosing device re-closing all three phases at once.

This mode is generally used on lines with strong interconnection between a power source and a load, or between two robust power systems.

There are two main methods to initiate automatic reclosing:

I. Non-Correspondence Initiation (Position Mismatch Start)

Non-correspondence initiation occurs when the control status of the circuit breaker does not match its actual position.

The protection device uses a breaker position input (typically the "trip position" contact) to determine the breaker's status. If this input is closed, it indicates the breaker is open. If the control switch is in the "closed" position at this time, it implies the breaker was previously closed. This mismatch between control and actual position triggers the reclosing function—known as "position mismatch initiation."

This method can initiate reclosing both for protective relay trips and for unintended breaker tripping ("stealth tripping").

Advantages: Simple and reliable.
Disadvantages: May fail to operate if position relay contacts are faulty or auxiliary breaker contacts are defective.

II. Protection-Based Initiation

Protection-based initiation refers to starting the reclosing process after the protective relay issues a trip command.

After a protective trip, the device detects loss of line current and initiates reclosing. Typically, the protection device also includes a digital input labeled "external trip to initiate reclosing," allowing the second protection set in a dual-redundant configuration to trigger reclosing in the first set.

This method simplifies reclosing configuration, as the protection software determines a fixed reclosing mode, making it simple and reliable.

It can effectively correct false trips caused by protection maloperation, but cannot correct unintended "stealth tripping" caused by the circuit breaker itself.

III. Summary

Protection-based initiation and non-correspondence initiation serve as complementary methods. Modern microprocessor-based protection relays typically incorporate both methods. Some advanced designs omit external mismatch contacts and instead initiate reclosing directly when, in the absence of an external trip command (e.g., manual or remote trip), the device detects a change from "closed" to "open" position.