A separately excited DC motor is supplied from 230V, 50Hz source through a single phase half wave controlled converter. It’s field is fed through single phase semiconverter with zero degree firing angle delay. Motor resistance Ra= 0.7Ω and Motor constant = 05V-sec/rad. For rated load torque of 15Nm at 1000 rpm and for constant ripple free current,

determine

a) Firing angle delay of the armature converter.

b) RMS value of thyristor current.

c) Input power factor of the armature converter.

Mumbai University > Electronics Engineering > Sem7 > Power Electronics 2

Marks: 10M

Year: Dec 2013

a) Motor constant=0.5 V.sec/rad = 0.5 Nm/A=$K_m$

But motor torque ,$T_e=K_m$

$\therefore$ Armature current = $\frac{15}{0.5}=30A$

Motor emf,

$E_a=K_m.ω_m=0.5\frac{2π \times 1000}{60}=52.36V$

For 1-phase half –wave converter feeding a dc motor,

Thus, firing – angle dristor current elay of converter 1 is $65.336^0$

(b) Rms value of thyristor current from equ. Is

$I_{Tr}=I_a\big(\frac{\pi - \alpha}{2\pi}\big)^{1/2}=30\big(\frac{180-65.336}{360}\big)^{1/2}=16.931A=I_{ar}$