1. Significance of Reclosing

In power systems, faults on transmission lines are common, and enhancing the reliability of these lines is crucial. Approximately 80%-90% of transmission line faults are transient, mainly caused by lightning, tree branch discharges, wind-induced line contact, bird interference, and contamination. These transient faults allow the arc to extinguish and insulation strength to restore, leading to self-clearing faults. If the circuit breaker is closed again, power can be restored, reducing outage time and improving reliability.

2. Disadvantages of Reclosing

While automatic reclosing increases reliability and system stability, it can also have adverse effects, such as causing short-circuit current surges during reclosing on permanent faults, which may lead to system oscillations and deteriorate breaker conditions.

3. Classification and Requirements

Reclosing devices can be classified as single-phase, three-phase, or comprehensive; they can also be categorized based on single or double actions, and by power source configuration. Requirements include starting based on control switch and breaker positions, preventing actions when conditions are unsafe, limiting the number of actions, automatic resetting, and accelerating protection actions when necessary.

4. Coordination with Protection

Coordination involves accelerating protection before and after reclosing. After a fault, selective protection should remove the faulted line while reclosing occurs. If a permanent fault is detected, the breaker should trip again without delay.

5. Four Types of Reclosing Methods

1. Inhibition Method: All phases trip without reclosing for any fault.

2. Single-Phase Reclosing: Automatically recloses a single phase after a single-phase fault, trips all phases for permanent faults.

3. Three-Phase Reclosing: Automatically recloses all phases for any fault, tripping all for permanent faults.

4. Comprehensive Reclosing: Single-phase faults trigger single-phase reclosing, while inter-phase faults lead to three-phase reclosing.

6. Protection Circuit Access

All protection must go through the reclosing device to trip the breaker, connecting different protections to specific terminals for various scenarios.

7. Capacitor-Based Automatic Reclosing

Capacitor-based devices can only recluse once due to their discharge and charge cycle, limiting their ability to re-engage after a permanent fault.

8. Reclosing Starting Circuit

The starting mechanism involves timers and relays that initiate the reclosing process upon fault detection and breaker tripping.