Static switch including surge suppressing means

Claim 2

A forced commutation static switch adapted to be connected between a voltage source and an electric power load comprising: a. a first thyristor switchable from a nonconductive state to a load current conducting state; b. commutation means connected in shunt with said first thyristor and adapted for rendering said first thyristor nonconductive upon command, said commutation means comprising: i. a second thyristor poled in the same direction as said first thyristor; and ii. a commutating capacitor in series with said second thyristor; c. charging means for charging said commutating capacitor to a voltage in the polarity tending to forward bias said second thyristor and reverse bias said first thyristor; and d. means separate from said charging means for protecting said first thyristor from reverse voltage surges when said first thyristor is nonconductive, said last mentioned means comprising a unipolarity conducting element connected in shunt with said second thyristor and poled in opposition thereto.

Claim 3

A forced commutation static switch adapted to be connected between a voltage source and an electric power load comprising: a. a first thyristor switchable from a nonconductive state to a load current conducting state; b. commutation means connected in shunt with said first thyristor and adapted for rendering said first thyristor nonconductive upon command, said commutation means comprising: i. a second thyristor poled in the same direction as said first thyristor; and ii. a commutating capacitor in series with said second thyristor; c. charging means for charging said commutating capacitor to a voltage in the polarity tending to forward bias said second thyristor and reverse bias said first thyristor; d. means for limiting the magnitude of the recovery voltage transient appearing across said first thyristor when it is rendered nonconductive by said commutation means, said transient magnitude limiting means being connected in shunt with said commutating capacitor and including: i. a resistor; and ii. a first unipolarity conducting element poled in the same direction as said first and second thyristors; and e. means separate from said charging means for protecting said first thyristor from reverse voltage surges when said first thyristor is nonconductive, said means comprising a second unipolarity conducting element connected in shunt with said second thyristor and poled in opposition thereto.

Claim 4

A forced commutation static switch adapted to be connected between a voltage source and an electric power load comprising: a. a first thyristor switchable from a nonconductive state to a load current conducting state; b. commutation means connected in shunt with said first thyristor and adapted for rendering said first thyristor nonconductive upon command, said commutation means comprising: i. a second thyristor poled in the same direction as said first thyristor; and ii. a commutating capacitor in series with said second thyristor; c. charging means for charging said commutating capacitor to a voltage in the polarity tending to forward bias said second thyristor and reverse bias said first thyristor; d. means for limiting the magnitude of the recovery voltage transient appearing across said first thyristor when it is rendered nonconductive by said commutation means, said transient magnitude limiting means being connected in shunt with said commutating capacitor and including: i. a resistor; and ii. a first unipolarity conducting element poled in the same direction as said first and second thyristors; and e. means separate from said charging means for protecting said first thyristor from reverse voltage surges when said first thyristor is nonconductive, said means comprising a second unipolarity conducting element connected in shunt with said second thyristor and poled in opposition thereto.