Title: Force commutated static isolator circuit

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Abstract: The invention provides a bilateral static isolator which is activated by "soft" forced commutation. Between two points in the power line to be interrupted are connected two thyristors in series-opposition, thus cathode to cathode. In antiparallel with each thyristor is mounted a diode. Thus, the two diodes appear in series opposition between the two power line points. A resonant circuit is applied to the conducting thyristor in order to turn it off with a relatively small reverse voltage. This voltage is obtained by resonant discharge of a precharged capacitor C through an inductor L and a diode D connected in reverse with the thyristor. The forward voltage drop of the diodes appears in reverse across the thyristors from the instant the discharge current rises above the line current until the instant the discharge current drops below the level of the line current. It is during this interval that the thyristor is provided with "soft" reverse bias. Subsequently the net current reverses again. With the thyristor now recovered, and the diode blocking, the current flows through the other diode and returns by the commutating branch associated therewith.


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