Which protection scheme is designed to trip all three phases together for a three-phase fault?

• A. Three-pole protection
• B. Single-pole protection
• C. Ground fault protection
• D. Phase-to-phase protection

Answer: (A)

The main idea is that a three-phase fault affects all three conductors at once, so the protection must remove power from all three lines at the same time. A three-pole protection scheme is built to trip all three poles of the circuit breaker simultaneously with a single trip signal. This ensures the fault current is interrupted on every phase, preventing a partially energized system, reducing circulating currents, and protecting equipment from uneven heating or severe stress. It also helps maintain system symmetry and stability as the fault is cleared.

Other schemes either trip only one phase at a time or focus on faults to ground or between phases, which isn’t sufficient to cleanly clear a three-phase fault. Tripping all three poles together is the most reliable way to fully isolate the fault and safeguard the network.