Auto-Reclosing Logic

The dead time is the intentional delay between the circuit breaker trip and the automatic reclose command. This interval allows the arc path of a transient fault to de-ionize. Typical settings range from 0.3 seconds for high-speed reclosing on transmission lines to 15-30 seconds on distribution feeders to coordinate with downstream fuse saving schemes. The dead time must exceed the fault de-ionization time to prevent re-striking the arc upon re-energization.

The reclaim timer starts immediately after a successful reclose. If the circuit breaker trips again before this timer expires, the relay logic interprets this as a permanent fault and proceeds to the next shot in the sequence or directly to lockout. Reclaim time is typically set between 10 and 60 seconds. A successful reclose that outlasts the reclaim period resets the shot counter to zero, restoring full auto-reclose readiness.

Most distribution reclosers execute a programmed sequence of up to four shots before locking out. A common sequence is 1 fast curve + 3 delayed curves (1F3D). The initial fast trip minimizes damage and outage time for temporary faults, while subsequent delayed trips allow downstream fuses to clear permanent faults selectively. Each shot can be programmed with distinct time-current characteristic curves and dead times.

For lines interconnecting two live sources, a sync-check relay supervises the auto-reclose command. It measures the voltage magnitude, frequency, and phase angle difference across the open breaker. The close is only permitted when parameters fall within programmable limits—typically voltage difference < 5%, frequency slip < 0.1 Hz, and phase angle < 20 degrees. This prevents out-of-synchronism closing that could damage generators and cause system instability.

In a zone-sequence coordination scheme, line reclosers and downstream sectionalizers work together without requiring communication. The recloser executes its multi-shot sequence. Sectionalizers count overcurrent pulses during the recloser's open intervals and open during a dead time after a preset count is reached. This isolates the faulted lateral while the recloser successfully restores the main trunk, minimizing the number of customers affected by a permanent fault.

When the programmed shot sequence is exhausted without a successful reclose, the relay enters lockout—the breaker remains permanently open until manual intervention. Lockout prevents repeated closing into a bolted fault, which subjects transformers and conductors to severe electromechanical stress. The lockout state is typically indicated locally via LED flags and communicated to the SCADA master station via DNP3 or IEC 61850 for operator dispatch.

An intelligent controller on a line recloser that executes multi-shot auto-reclosing sequences, coordinates with downstream sectionalizers, and isolates permanent faults on overhead distribution feeders. Key functions include:

• Configurable dead time between shots
• Reclaim time management to reset the sequence counter
• Coordination with fuse-saving and fuse-blowing strategies
• Integration with SCADA for remote lockout indication

An engineering analysis that selects pickup currents, time multiplier settings, and curve shapes to ensure the protective device closest to a fault trips first, maintaining selectivity and minimizing service disruption. For auto-reclosing schemes, coordination studies must account for:

• Cold load pickup after extended outages
• Inrush currents during re-energization
• Fuse saving vs. fuse blowing philosophies
• Coordination margins across multiple reclosing attempts

The intentional delay between a circuit breaker trip and the initiation of a reclose command. Dead time allows for:

• Arc deionization in the fault path so transient faults can self-extinguish
• System inertia to stabilize before re-energization
• Communication with remote terminals in teleprotection schemes

Typical dead times range from 0.3 to 30 seconds, with shorter times for transmission lines and longer delays for distribution feeders serving motor loads.

A timer that starts after a successful reclose. If the breaker trips again within this window, the reclosing relay advances to the next shot in the sequence rather than resetting. If the reclaim time expires without a trip, the sequence counter resets to shot 1. This mechanism:

• Prevents indefinite cycling on intermittent faults
• Distinguishes between a new fault and a re-strike of the original fault
• Typically set between 10 and 180 seconds depending on system characteristics

The identification of faults where a conductor contacts a high-resistance surface, producing low fault currents that conventional overcurrent protection cannot easily distinguish from normal load. These faults pose a challenge for auto-reclosing because:

• Fault current may be below the pickup threshold, so no trip occurs
• If detected, reclosing onto a downed conductor creates a public safety hazard
• Modern relays use waveform pattern recognition and harmonic analysis to detect HIFs
• Auto-reclosing is typically blocked when HIF is identified