<p>The circuit (1) introduced between the six-pulse thyristor bridge (2) and the DC intermediate (link) circuit (6) includes three extinction thyristors (TL+) connected directly to the secondary windings (LTr) of the input transformer (4). Energy stored in these or other inductors can be dissipated in a circuit comprising a free-wheel diode (DF) and resistor (RF), and an extinction capacitor (CL) and thyristor (TL-). Detection of a commutation (switching) fault instigates a short firing command of typically 200 microns duration to all of the extinction thyristors, while the others are blocked in common with the GTO thyristor following the DC voltage link circuit.</p>
