Commutation directing circuit for fault current limiting static switch

Claim 2

In a power system including a thyristor switch comprising a pair of power thyristors connected in inverse parallel relationship with one another, said thyristors being adapted to alternately conduct current between an alternating voltage source and a load, fault current detecting means for providing a ''''Stop'''' signal in response to the magnitude of current through said switch attaining a preselected level, and first and second triggerable commutation means respectively connected to said power thyristors, improved commutation control means comprising: first means operative when actuated for triggering said first commutation means, second means operative when actuated for triggering said second commutation means, both of said first and second triggering means being coupled to said fault current detecting means for actuation by said ''''Stop'''' signal, polarity detecting means coupled to said switch for determining which one of said power thyristors is conducting and for providing signals indicative thereof, and means connected to both of said triggering means and to the polarity detecting means and responsive to the signals from said polarity detecting means for selectively enabling the triggering means of the commutating means connected to the conducting power thyristor to be actuated by said ''''Stop'''' signal while disabling the other triggering means from being actuated, said last mentioned means comprising: first switch means coupled to the first triggering means and operative when conductive for directing the ''''Stop'''' signal away from the first triggering means; and second switch means coupled to the second triggering means and operative when conductive for directing the ''''Stop'''' signal away from said second triggering means.

Claim 3

The commutation control circuit as specified in claim 1 wherein said switch means are controllable in response to signals from said polarity detecting means.

Claim 4

The commutation control circuit as specified in claim 2 wherein said polarity detecting means is responsive to the direction of current in said switch only when the magnitude thereof exceeds a predetermined threshold level.

Claim 5

The commutation control circuit as specified in claim 3 wherein each of said first and second switch means is a transistor connected in shunt with said first and second triggering means, respectively.

Claim 6

In a power system including a thyristor switch comprising a pair of power thyristors connected in inverse parallel relationship with one another, said thyristors being adapted to alternately conduct current between an alternating voltage source and a load, current sensing means for monitoring the current flowing through the switch, fault current detecting means for providing a Stop signal in response to the magnitude of said current attaining a preselected level, a first commutation circuit connected in shunt with one of said power thyristor, a second commutation circuit connected in shunt with the other power thyristor, each commutation circuit comprising a d.c. charged commutating capacitor and a normally non-conductive commutating thyristor poled in the direction of the power thyristor shunted, improved commutation control means comprising: first trigger means operative when actuated for supplying a trigger signal to the commutating thyristor in shunt with the first power thyristor, second trigger means operative when actuated for supplying a trigger signal to the commutating thyristor in shunt with the other power thyristor, both of said first and second trigger means being coupled to said fault current detecting means for actuation by said ''''Stop'''' signal, polarity detecting means connected to said current sensing means for determining which power thyristor is conducting and for providing signals indicative thereof, and directing means connected to the polarity detecting means and responsive to the signals therefrom for directing the Stop signal to the trigger means of the commutating thyristor shunting the conducting thyristor while preventing other trigger means from receiving that signal, whereupon only the commutation circuit shunting the conducting thyristor is operative for interrupting the fault current, said directing means comprising first controllable switch means coupled to the first trigger means and operative when conductive for directing the ''''Stop'''' signal away from said first trigger means; and second controllable switch means coupled to the second trigger means and operative when conductive for directing the Stop signal away from said second trigger means.

Claim 7

In a power system including a thyristor switch comprising a pair of power thyristors connected in inverse parallel relationship with one another, said thyristors being adapted to alternately conduct current between an alternating voltage source and a load, current sensing means for monitoring the current flowing through the switch, fault current detecting means for providing a Stop signal in response to the magnitude of said current attaining a preselected level, a first commutation circuit connected in shunt with one of said power thyristor, a second commutation circuit connected in shunt with the other power thyristor, each commutation circuit comprising a d.c. charged commutating capacitor and a normally non-conductive commutating thyristor poled in the direction of the power thyristor shunted, improved commutation control means comprising: first trigger means operative when actuated for supplying a trigger signal to the commutating thyristor in shunt with the first power thyristor, second trigger means operative when actuated for supplying a trigger signal to the commutating thyristor in shunt with the other power thyristor, both of said first and second trigger means being coupled to said fault current detecting means for actuation by said ''''Stop'''' signal, polarity detecting means connected to said current sensing means for determining which power thyristor is conducting and for providing signals indicative thereof, and directing means connected to the polarity detecting means and responsive to the signals therefrom for directing the Stop signal to the trigger means of the commutating thyristor shunting the conducting thyristor while preventing other trigger means from receiving that signal, whereupon only the commutation circuit shunting the conducting thyristor is operative for interrupting the fault current, said directing means comprising first controllable switch means coupled to the first trigger means and operative when conductive for directing the ''''Stop'''' signal away from said first trigger means; and second controllable switch means coupled to the second trigger means and operative when conductive for directing the Stop signal away from said second trigger means.

Claim 8

The commutation control circuit as specified in claim 5 wherein said polarity detecting means is responsive to the direction of current in said switch only when the magnitude thereof exceeds a predetermined threshold level.