In high-voltage AC transmission lines

accurately predicting the zero crossing of current is crucial for determining the optimal timing for circuit breaker operations to interrupt fault currents near this point.Two factors contribute to the drift of the fault current zero point from the expected steady-state short circuit current.Two main factors contribute to the zero drift of the fault current from the expected steady-state short-circuit current.The first factor is the superimposition of the decaying DC component on the AC component during the transient process in the initially interrupted phase

causing zero drift.The second factor involves different zero crossing times of the three-phase currents;when an arc extinguishes in one phase of the circuit breaker

it alters the topology of the entire three-phase circuit

resulting in zero drift in the other two phases.This study shows that in both grounded and ungrounded systems

under various short circuit fault conditions

the zero point of the next interrupted phase advances after the first phase interruption

while the last phases zero point shifts backward.These conclusions provide a theoretical basis for determining the timing of relay protection device actions.