High voltage converter apparatus having overvoltage protection circuits for thyristors

Claim 1

In a high voltage converter apparatus including a plurality of tray modules constituting one arm thereof, each tray module comprising: a plurality of thyristors connected in series; an ignition circuit for generating an ignition signal for said thyristors; a pulse transformer having a primary winding and a plurality of secondary windings, said primary winding being connected to said ignition circuit and each of said secondary windings being connected between a gate and a cathode of a corresponding one of said thyristors; a plurality of voltage dividing circuits, each of said voltage dividing circuits including an impedance element and being connected in parallel with a corresponding one of said thyristors; a plurality of forward overvoltage protection circuits, each of said forward overvoltage protection circuits being connected between an anode and a gate of a corresponding one of said thyristors; means, including a plurality of temperature relays each provided in a corresponding one of said voltage dividing circuits, for short-circuiting the gate-cathode path of the associated thyristor when the temperature of the corresponding impedance element included in each of said voltage dividing circuits exceeds a predetermined value; a plurality of overvoltage detectors, each connected in parallel with a corresponding one of said thyristors and having a detection level which is lower than the operating voltage of said overvoltage protection circuit and higher than the shared voltage of each of said thyristors during its normal operation for detecting an overvoltage condition in the corresponding thyristor; and high level detector means for generating a stopping instruction signal under such a condition that all of said overvoltage detectors detect simultaneously an overvoltage condition a predetermined number of repetition times.