Question

For the commutation circuit shown below, with C = 10 $\mu F$ and L = 8 $\mu H$. The initial voltage across capacitor is 220 V and load current is constant at 200 A. The value of time required to turn off main thyristor after the auxiliary thyristor is turned on (in $\mu sec)$ will be________

Answer 1

Time required to turn-off main thyristor after Auxiliary thyristor is turned on

$\left(t_{cm}\right)=\pi \sqrt{LC}+\sqrt{LC}.si{n}^{-1}\left(\frac{I_0}{I_P}\right)$

$I_p=V_S\sqrt{\frac{C}{L}}=200\sqrt{\frac{10\times {10}^{-6}}{8\times {10}^{-6}}}=245.969A$

$t_{cm}=\left(\pi \sqrt{80\times {10}^{-12}}\right)+\sqrt{80\times {10}^{-12}}si{n}^{-1}\left(\frac{200}{245.967}\right)$

$=(\pi \times 8.944\times {10}^{-6})+8.944\times {10}^{-6}si{n}^{-1}\left(0.813\right)\times \frac{\pi }{180}$

$t_{cm}=36.59\mu sec$