The basic operation principle of thyristor control drives is adjustment of motor speed through modifying the rotor resistance within wound rotor motors.
Stator
Stator control circuit contains of a thyristor reverser. The direction of shaft rotation is modified by means of switching between the two phases. The motor current is controlled by two phases using a current transformers. The DVESLY drive ensures motor protection against thermal overloads and short-circuit current.
Rotor
Rotor circuit resistance is commuted through thyristor commutators. Depending on the load on shaft, the thyristors can be arranged in a triangle or in an antiparallel connection.
The rotor phases are commuted in line with the signals received from the crane operator control units.