North Carolina ElectriCities Intermediate Lineworker Practice Exam

Where are donut-shaped current transformers typically located?

around the bushings of circuit breakers and power transformers in the control room in the substation yard away from equipment near the cooling fans

Correct Answer:

around the bushings of circuit breakers and power transformers

Explanation:

Donut-shaped current transformers are placed around the actual conductors feeding high‑voltage equipment, typically at the bushings of circuit breakers and power transformers. Placing the toroidal core around the conductor lets the transformer sense the true line current as it enters or leaves that equipment, providing accurate measurement for protection relays and metering while keeping the sensing circuitry safely isolated from high voltage. Installing them in the control room or away from equipment wouldn’t capture the real current flow or allow proper protection, and placing them near cooling fans wouldn’t serve the sensing needs.

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