Question

A voltage commutation circuit shown below has the value of capacitor C if each thyristor has turn off time of 50 $\mu$s is


$V_s=250V,$ $\text{safty margin=2,}$ $R_1=20\Omega and{R}_2=30\Omega$

Answer 1

$V_s=250V{R}_1=20\Omega and{R}_2=30\Omega$

Capacitance, $C=\frac{t_{c1}}{R_{1}ln2}=\frac{2\times 50\times {10}^{-6}}{20\times ln2}=7.21\mu F$

$C=\frac{t_{c2}}{R_{2}ln2}=\frac{2\times 50\times {10}^{-6}}{30\times ln2}=4.8\mu F$

So, choose the biggest one i.e. 7.21 $\mu F$