Suojareleet

Suojareleet, the Finnish term for protective relays, are electrical protection devices used in power systems to detect abnormal conditions and initiate isolation of faults to protect equipment and maintain system stability. They monitor electrical quantities such as current, voltage and frequency using sensors like current transformers and voltage transformers, and compare measured values with predefined settings. When a fault or abnormal condition is detected, the relay can energize a trip or close command to circuit breakers, often coordinating with other protection devices to ensure selective tripping.

Protective relays come in several types, including overcurrent relays, differential relays, distance (impedance) relays, and earth-fault relays, as well as motor protection and protections for under/over-voltage and under/over-frequency. Historically, electromechanical relays were common, but digital or numerical relays have largely supplanted them, offering advanced algorithms, self-diagnostics and improved communication capabilities.

A typical suojareleet system consists of input sensors, the relay logic unit, and outputs that actuate circuit breakers. Modern systems may include programmable logic, web-based or embedded diagnostics, and network communication interfaces. In practice, protective relays are integral to substation automation and power system protection schemes, ensuring rapid fault isolation, limiting equipment damage, and reducing outage durations.

Standards and integration: Protection relays are designed to comply with international standards and often communicate using protocols such as IEC 61850, IEC 60870-5, and related equipment standards. In Finland, as in many countries, suojareleet are deployed across generation, transmission and distribution networks to enhance reliability and safety.