A voltage commutated thyristor chopper circuit is shown in fig. The chopper is operated at $$500$$ $$Hz$$ with $$50\% $$ duty ratio. The load takes a constant current of $$20A$$

(a) Evaluate the circuit turn off time for the main thyristor $$T{h_1}$$
(b) Calculate the value of inductor $$L,$$ if the peak current through the main thyristor $$Th,$$ is limited to $$180$$% of the load current.
(c)Calculate the maximum instantaneous output voltage of the chopper

A $$dc$$ motor with armature resistance $${R_a}$$ is fed from a step down chopper in the continuous mode, and operates at some known speed and known excitation current. The motor current rises from $${I_{\min }}\,\,$$ to $${I_{\max }}\,\,$$ in the $${T_{on}}$$ period Ton of the chopper; and drops from $${I_{\max }}\,\,$$ to $${I_{\min }}\,\,$$ in the $${T_{off}}$$ period Toff of the same circuit. Both the rise and fall of the current may be assumed to be approximately linear. What is the average power loss in the machine armature?