What equipment is typically used to implement ground fault protection on feeders and buses?

• A. Ultrasonic sensors for audible noise.
• B. Current transformers and relays.
• C. Magnetic field detectors.
• D. Temperature sensors and fans.

Answer: (B)

Ground fault protection on feeders and buses works by sensing leakage current and quickly tripping to clear the fault. Current transformers are wrapped around the conductors to produce a scaled secondary current that represents the actual line current. A protective relay monitors the sum of the phase currents (and the neutral if used); under normal operation this sum is zero. If current starts leaking to ground due to a fault, the residual current becomes nonzero, and the relay trips the associated breaker to disconnect the defective section. This combination of current transformers and relays is specifically designed to detect ground faults, unlike the other options which relate to monitoring noise, magnetic fields unrelated to fault current, or cooling rather than electrical protection.