Which relay is frequently used to protect transformers and busses?

Study for the NERC Transmission Operations (TOP) Exam with our multiple choice questions and comprehensive explanations. Prepare effectively and boost your confidence for test day!

The selection of the differential relay, identified as the #87 relay, as the correct answer is grounded in its fundamental design and application in electrical protection schemes. Differential relays are essential for protecting transformers and bus systems because they effectively detect internal faults.

The #87 differential relay operates by comparing the current entering a device (like a transformer or bus) with the current leaving it. In a healthy system where there are no faults, these currents should be nearly equal. If the relay detects a significant difference between the incoming and outgoing currents, it indicates a fault within the transformer or bus. This capability allows for rapid isolation of faulty equipment, minimizing damage, and maintaining system stability.

Moreover, the use of the #87 relay is vital in systems where the high impedance can lead to misoperation of other types of relays. The differential relay specifically targets faults occurring within the protected zone, resulting in high sensitivity and selectivity—important traits for transformer and bus protection. In addition, the relay can be used effectively for phase and ground protection in various configurations of transformers and buses, further underscoring its versatility and critical role in system reliability and safety.

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