A 3-phase 6-pulse converter is operated from a three-phase delta- connected 230 V, 50 Hz supply to supply a separately excited DC motor. The motor is rated at 220 V, 600 rpm, 500 A and it has an armature resistance of 0.02 02. (i) Draw the circuit diagram of the system, and state what electronic component is used for the converter. Explain how this component works. (ii) Calculate the delay angle a. (iii) Calculate the delivered torque at rated conditions. (iv) If the mechanical loss torque is 150 Nm, and the power lost in the field winding is 3500 W. Calculate the full load efficiency of the motor.

3. A three phase bridge rectifier is supplied by 380 Volt line voltage through a Star/delta connected transformer of which turns ratio is 1. The firing delay angle is a=30° and the load is resistive R=2.2 Ohm. Draw the circuit diagram and mark the followings on this figure : average values of output voltage, the currents and voltages of each transformer leg.

What makes buck converters preferable to regulators?