Recloser Control

The core function of a recloser control, executing a programmable sequence of trip-and-reclose cycles to clear transient faults. A typical sequence might include one fast curve trip followed by two delayed curve trips before locking out on a permanent fault.

• Fast Curve: Trips instantaneously for high-magnitude faults to minimize damage
• Delayed Curve: Allows downstream fuses to clear before the recloser operates
• Dead Time: Configurable interval (typically 0.5–30 seconds) between reclose attempts
• Reclaim Time: A reset window after successful reclose; if a fault recurs within this period, the control advances to the next shot in the sequence
• Lockout: Permanent open state after exhausting all programmed shots, requiring manual intervention

Modern recloser controls incorporate directional phase and ground overcurrent elements that determine fault direction using a polarizing quantity—typically zero-sequence voltage for ground faults and quadrature voltage for phase faults. This enables selective coordination in looped or networked distribution feeders where fault current can flow in either direction.

• Forward/Reverse Discrimination: Trips only for faults downstream of the recloser, preventing unnecessary lockouts for upstream events
• 67/67N Elements: Standard ANSI device numbers for directional phase and ground protection
• Polarizing Methods: Zero-sequence voltage, negative-sequence voltage, or cross-phase voltage techniques
• Coordination with Distributed Generation: Essential for feeders with bidirectional fault current from solar or battery storage

Advanced recloser controls support IEC 61850 Generic Object Oriented Substation Event (GOOSE) messaging, enabling high-speed, peer-to-peer communication with downstream sectionalizers, upstream breakers, and adjacent reclosers over Ethernet.

• Transfer Trip Schemes: A downstream device detecting a fault can send a GOOSE message to the recloser to accelerate tripping
• Blocking Schemes: Prevents the recloser from operating when a downstream device is already clearing the fault
• Latency: GOOSE messages are transmitted within 4 milliseconds, meeting protection-grade speed requirements
• Auto-Restoration Logic: Coordinates multiple devices to isolate the faulted section and restore power to healthy laterals without SCADA intervention

Recloser controls can store multiple settings groups and dynamically switch between them based on real-time grid conditions. This is critical for feeders with high penetration of distributed energy resources (DERs) where fault current levels and direction vary significantly.

• Time-of-Day Profiles: Switch to lower pickup settings during light load periods
• Generation-Dependent Groups: Automatically activate settings optimized for high DER output when generation is online
• Topology-Triggered Switching: Change settings when a normally-open tie point closes, altering the feeder configuration
• Cold Load Pickup Logic: Temporarily raise pickup thresholds after an extended outage to accommodate inrush current from thermostatically controlled loads

Conventional overcurrent protection often fails to detect high-impedance faults (HIF) where a downed conductor contacts a high-resistance surface like asphalt, sand, or dry grass. Modern recloser controls employ specialized algorithms to identify the chaotic, non-linear arcing signatures characteristic of HIFs.

• Harmonic Content Analysis: Monitors for elevated odd-order harmonics and inter-harmonics produced by intermittent arcing
• Randomness Detection: Identifies the bursty, non-stationary current waveform patterns unique to HIFs
• Sensitivity Settings: Configurable thresholds to balance detection probability against nuisance tripping from load switching
• Safety Application: Primarily deployed for public safety on feeders traversing urban or high-pedestrian areas

Integrated Digital Fault Recorder (DFR) functionality captures high-resolution voltage and current waveforms during disturbances, storing them in the IEEE C37.111 COMTRADE format for post-fault analysis.

• Sampling Rate: Typically 16–128 samples per cycle, capturing harmonics up to the 50th order
• Trigger Sources: Configurable to trigger on protection element pickup, trip, external contact closure, or manual command
• Pre-Fault Data: Records several cycles of pre-trigger data to establish steady-state conditions
• Remote Retrieval: COMTRADE files can be automatically uploaded via FTP or DNP3 file transfer to a central analysis server
• Sequence-of-Events (SOE): Time-stamped log of all internal state changes with 1-millisecond resolution for coordination audits

The programmable sequence that defines how a recloser responds to a fault. It specifies the number of reclose attempts (shots), the dead time between trip and reclose, and the reclaim time that resets the cycle. A typical sequence might be 1 fast curve trip followed by 2 delayed curve trips before lockout. This logic distinguishes transient faults, like a tree branch touching a line, from permanent faults, like a broken conductor, preventing unnecessary sustained outages.

Two conflicting philosophies for coordinating reclosers with downstream fuses. Fuse saving uses an instantaneous recloser trip to clear a temporary fault before the fuse element melts, preventing a permanent fuse operation. Fuse blowing allows the fuse to operate for permanent faults, using the recloser's delayed curve only as backup. Modern recloser controls often implement sequence coordination, switching from a fuse-saving fast curve on the first shot to a fuse-blowing delayed curve on subsequent shots.

The phenomenon where the inrush current after a prolonged outage is significantly higher than normal load. When a recloser restores power after an extended dead time, thermostatically controlled loads like air conditioners and refrigerators all start simultaneously, creating a diversity factor of 1.0. Recloser controls must temporarily raise the overcurrent pickup threshold or block sensitive earth fault elements to avoid nuisance tripping on this inrush, a function often called cold load pickup logic.

The challenge of detecting a downed conductor on a high-resistance surface like asphalt or dry soil. The resulting fault current is often below the recloser's minimum pickup, appearing as normal load. Advanced recloser controls use waveform analytics to identify the chaotic, non-linear current signatures characteristic of arcing. Algorithms analyze inter-harmonics, asymmetry, and random burst patterns to declare a high-impedance fault and trip, a critical safety function for public protection.