Suojarele

Suojarele, a Finnish term meaning protective relay, is an automatic protective device used in electrical power systems to detect abnormal conditions and initiate protective actions. Its primary purpose is to isolate faulty parts of the network to prevent equipment damage, maintain system stability, and enhance safety.

Historically, protection relied on electromechanical relays. In recent decades, relays have evolved into solid-state and digital (numerical) devices. Modern suojarele often combine multiple protection functions in a single unit, offer self-testing, and communicate with supervisory and automation systems. They may be deployed at substations, on transformers, feeders, and generation facilities, and are integrated into broader protection and control schemes.

A suojarele monitors electrical quantities such as current, voltage, frequency, and power quality. When these quantities exceed preset thresholds or follow certain patterns, the relay activates a trip or close command to circuit breakers. Common protection functions include overcurrent protection, distance (impedance) protection, differential protection, ground-fault protection, and under/over voltage or frequency protection. Directional logic, time grading, and coordination with other relays ensure selective tripping to minimize disruption.

In operation, suojarele are part of a protection scheme designed for reliability and selectivity. Settings are chosen to ensure the fastest, safest response to actual faults while avoiding nuisance trips. Modern implementations often use standardized communication protocols, such as IEC 61850, to integrate protection, automation, and monitoring across substations and grids.