DC voltage of the generator field winding by a three-phase thyristor rectifier provided later. In the same period incorrect, out of step, system failure, etc., the rectifier wi
ll cause hazardous elements and the field winding on the DC side over-voltage insulation, this must limit over-voltage, commonly used as shown in Fig. 13-90 protection circuit. Figure, BQ as excitation windings. Varistor R, as a back-up over-voltage protection element.