Its main purpose is to safeguard electrical equipment like transformers, generators, and transmission lines from damage due to abnormal conditions such as overloads, short circuits, or voltage imbalances. Engineering use: Relays are used in control panels, motor circuits, PLC interfaces, alarms, breaker trip circuits, and power system protection schemes. What controls it: Relay selection. Imagine a sophisticated sentry continuously monitoring electrical parameters like current, voltage, and frequency. That's essentially what a protection relay does. These devices help ensure that electrical systems operate safely, preventing damage to both equipment and infrastructure.