What is the function of a protective relay in electrical systems?

• A. A device that converts AC to DC for protection
• B. A relay that detects abnormal conditions and triggers disconnection to protect equipment.
• C. A switch that permanently disconnects on power-up
• D. A device that reduces voltage during fault

Answer: (B)

Protective relays serve as the sensing and decision-making part of an electrical protection scheme. They continuously monitor electrical signals such as current, voltage, and sometimes frequency or impedance. When a measured value goes beyond its preset limits—for example, an overload, short circuit, or ground fault—the relay triggers a circuit breaker to open and isolate the faulty portion of the system. This rapid disconnection protects equipment from damage and helps keep the rest of the system safe and stable. Relays can be electro-mechanical, solid-state, or digital and may include time delays or coordination logic to avoid unnecessary trips. They don’t convert AC to DC, they don’t permanently disconnect on power-up, and they don’t function to reduce voltage during a fault; their role is to detect abnormal conditions and initiate disconnection through the breaker.