A proper operating protective relay scheme should normally operate for what conditions?

A proper operating protective relay scheme is designed to maintain system stability and protect equipment by detecting abnormal conditions, such as faults that occur in the power system. The primary purpose of protective relays is to identify faults—such as short circuits or equipment failures—and initiate protective actions to isolate the affected portions of the system. This helps to prevent damage to equipment, maintain system reliability, and ensure safety.

In the context of the choices provided, focusing on faulted system facilities aligns with the primary function of protective relay schemes. These relays are calibrated to respond to significant anomalies that can cause permanent damage or compromise the overall integrity of the electrical system, thereby enabling swift corrective action by shutting down or isolating the problematic areas.

While minor system disturbances, recoverable system power swings, and brief overloads may lead to operational challenges, they typically do not warrant the same kind of immediate intervention as fault conditions do. Protective relays are designed to avoid unnecessary tripping during transient conditions that are expected to self-correct, thus ensuring that normal operations can resume without undue interruptions.