Schweitzer Engineering Laboratories, Inc. SEL-551 Overcurrent Relay

The SEL-551 Overcurrent/Reclosing Relay from Schweitzer Engineering Laboratories is a protection relay designed to provide fast overcurrent protection for distribution feeders and to automatically reclose after a fault, minimizing outage duration. This unit combines phase and ground overcurrent protection elements with a built-in reclosing block, enabling it to detect faults, trip the circuit breaker, and reclose automatically when the fault has cleared. It accepts current inputs from protective current transformers and provides trip and close outputs to the connected breaker, with configurable pickup settings and time‑current characteristics that can be tailored to the protected circuit. The device records fault events, metering data, and disturbance information for post‑fault analysis, and it can be integrated with SEL protection and control ecosystems to coordinate protection, automation, and monitoring across a feeder or substation. The SEL‑551 family (including the SEL‑551C variant) is widely deployed in distribution protection schemes for feeders and bus protections, offering reliable performance in both substation and pole‑top switchgear environments, with support for field configuration and testing through standard SEL tools.