During a phase-to-phase fault in a three-phase power distribution transformer with Y-Δ connection, which mechanism causes sympathetic tripping of upstream circuit breakers?

💡 Explanation

Sympathetic tripping arises because the zero sequence current propagates rapidly through the Y-connected primary during a ground fault, creating current imbalance; therefore, breakers trip, rather than alternative over-voltages in the delta winding causing alternative harmonic injections.

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