Short Fault Current Zero Point Drift and Phase-Controlled Interruption Strategy in Three-Phase Power Transmission Lines

Accurate prediction of the current zero point is necessary for phase-controlled interruption of short fault current in three-phase high-voltage lines. There are two factors that contribute to the short fault currents zero drift in relation to the expected steady-state short-circuit currents. One factor is that when a short-circuit fault occurs a decayed DC component of fault current superposes on the AC component during transient process. The other factor is that three-phase currents have various zero timings, when one phase arc in the breaker is extinguished, the circuit topology of the other two phases changes, resulting in a new transient process once more. Analyzing shows if circuit breaker is switched off after short circuit fault has reached steady state, in three-phase network with isolated neutral, the first open phase will be interrupted, then the other two phases will be interrupted in the same time 1/4 power frequency cycle later. While in three-phase network with grounded neutral, the first open phase will be interrupted, then the second open phase interrupted about 76˚ later, finally the last open phase will be interrupted lagging additional 33˚. Research indicates that under various short-circuit fault conditions, after the first open phase being interrupted, the second open current zero point will shift forward and the last open phase zero point will shift backward.