a) A separately excited DC motor which is used in the EuRAIL system is fed from a three-phase six-pulse fully controlled bridge converter. The motor develops its full load torque at a rated speed of 1800 rpm taking a current of 60 A from a 400 V, 50 Hz supply. The armature resistance is 0.4 N and thyristors are ideal. Determine the following: 3 Vm cos a [You are given the armature voltage Va = (i) The rms value of the supply voltage if the motor runs at its rated conditions for the firing angle a=0. (ii) Obtain the range of firing angles for speed control of 1800 to 900 rpm. Assume the motor runs at full load torque. (iii) For the closed loop control operation of a drive system, you are given the following drives: a) Semi converter drive b) Full converter drive c) Dual- converter drive. Among the three mentioned drives above, which one you strongly recommend and why? [ Give five valid reasons] b) The EURAIL system has a three-phase DC variable speed drive (a six-pulse bridge converter) working on a 400 V 50 Hz supply feeds a DC motor manufactured by ABB, Made in France whose name plate details are shown in Figure Q2 (b). The motor drives a load having a torque speed characteristic given by TL =0.640. %3D ABB Motor Sep. 06-1995 IEC 34-1-1969 Type DMP 112-4L No 1124 01659 12.5 1500 rimin Duty S1 Ins. Class Arm. 495 Arm. 29.9 A Exc. 300 Exc. 2.18 IP 23S IC 06 IM 1001 Cat. No. FR 159 101-1A 123.5 kg MADE IN FRANCE FABRIQUE EN FRANCE Figure Q2(b) (i) Calculate the armature resistance. (ii) Calculate the firing angle for motor to run at 500 rpm and deliver full load torque. (iii) Calculate the efficiency of the DC motor running as stated in part (ii).