Which of the following statements about modern protective relays is accurate?

• A. They only provide overcurrent protection.
• B. They only monitor voltage.
• C. Fault detection and communications features are common.
• D. They are rarely used in modern systems.

Answer: (C)

Modern protective relays are multifunction devices that combine protection, monitoring, and communication. They do more than just overcurrent protection; they use a variety of protection schemes (like differential, distance, and directional overcurrent) and continuously monitor current, voltage, frequency, and phase relationships to detect faults and control breakers as needed. They also include self-diagnostic and event-recording features, and they communicate with other equipment and control systems through standard protocols, enabling remote monitoring, SCADA integration, and coordinated protection schemes. Because of these capabilities, fault detection and communications features are common. The other ideas—that they only provide overcurrent protection or only monitor voltage, or that they’re rarely used—don’t fit modern systems, which rely on their broad protections, monitoring, and networked control.