Automatic circuit reclosers enhance the protection of distribution circuits by interrupting and auto-reclosing an AC circuit according to a preset sequence. They effectively manage temporary faults on overhead distribution lines, often caused by tree limbs or wildlife, by briefly disrupting service to improve overall reliability. However, contact with reclosers or energized broken conductors on the ground can pose serious hazards.
A comprehensive protection scheme for radial distribution circuits integrates fuses, reclosers, and time-delay overcurrent relays. These relays, often characterized by an extremely inverse time-current curve, are designed to coordinate with reclosers and type T fuses. The relay settings prioritize recloser operations to clear faults before the relays activate. If the fault persists, the recloser eventually locks out after multiple attempts, allowing fuses to address downstream faults. Time-delay overcurrent relays then open the substation breaker after multiple recloser operations.
This coordination is visualized using time-current curves. Type T fuses are selected based on maximum tap loads to ensure proper coordination with reclosers. Reclosers are set with minimum trip ratings based on the maximum load current, thereby overriding cold load pickup. They typically perform two fast operations followed by two delayed ones, allowing temporary faults to clear themselves and enabling downstream fuses to clear permanent faults.
Effective protection in radial systems depends on the meticulous coordination of overcurrent relays and a thorough understanding of system behavior under various fault conditions. This coordination ensures that faults are isolated efficiently, minimizing the impact on the system and maintaining reliability. Modern digital reclosers and relays further enhance this coordination by providing advanced features such as real-time monitoring, communication capabilities, and precise timing adjustments, contributing to the overall stability and protection of the power system.
