One of the dominant factor in phase controlled switching is the determination of optimal switching phase, while the optimal switching phase is mainly affected by the pre-strike characteristics of the circuit breaker.

Appling the fitting expression to the calculation of the pre-strike characteristic, the variation rule of the withstand voltage of vacuum interrupters is thus reached according to the closing dynamic characteristic, through .

Prebreakdown Characteristics between Electrodes in Vacuum;

In comparison with devices fabricated by normal gate process,the dielectric defined gate devices show advantages in on-state breakdown,power performance.

The waveform controlled dc was applied to the sensor and the prebreakdown current flowing through the sensor was measured by the picoammeter.