Vacuum circuit breaker comprising series connected vacuum interrupters and capacitive voltage-distribution means

A multi-break alternating-current vacuum circuit breaker comprising:

• (a) a plurality of vacuum-type circuit interrupters,
• (b) means for connecting said interrupters electrically in series,
• (c) means for controlling the distribution of voltage appearing across said series combination of interrupters comprising a plurality of capacitive circuits respectively connected across said vacuum interrupters, the capacitive circuits having sufficient impedance as to exert no significant effect on the rate of rise of recovery voltage appearing across the circuit breaker after interruption,
• (d) the capacitive circuit across one of said interrupters comprising:
• (d.sub.1) the series combination of a relatively large main capacitor and a resistor connected across said one interrupter, and
• (d.sub.2) a relatively small auxiliary capacitor external to said one interrupter and connected across said one interrupter in parallel with said series combination of main capacitor and resistor,
• (e) the circuit loop comprising said one vacuum interrupter and said auxiliary capacitor connected thereacross being underdamped so that discharge of said auxiliary capacitor through said one interrupter upon spark-over of said one interrupter results in an oscillatory current through said circuit loop that produces a natural current zero through said one interrupter and clearance by said one interrupter at said natural current zero well before said main capacitor has had time to fully discharge through said one sparked-over interrupter.