Question

A single phase fully controlled bridge is supplied with 120 V, rms sinusoidal supply of 50 Hz. If the load current is continuous and individual thyristor voltage drop is 1.5 V. The value of peak voltage across each thyristor and mean load voltage for a firing angle of 45° will be respectively

• A. 169.71 V, 42.66 V
• B. 169.71 V, 73.39 V
• C. 196.42 V, 42.66 V
• D. 196.42 V, 73.39 V

Answer 1

The correct option is B 169.71 V, 73.39 V

For a single phase fully controlled bridge circuit

$V_{mean}=\frac{2}{\pi }\times V_m\cos \alpha -2V_T$
Where, $V_m$ is peak, sinusoidal value, $\alpha$ is firing angle and $V_T$ is thyristor voltage drop

For $V_m=120\sqrt{2}V,$

$\alpha =45{}^{\circ }$

$V_{mean}=\frac{2}{\pi }\times 120\sqrt{2}\cos 45{}^{\circ }-2\times \left(1.5\right)$

$=\frac{2}{\pi }\times 120\sqrt{2}\times \frac{1}{\sqrt{2}}-3=73.39V$

Peak value of voltage across each thyristor $=V_{max}$

$=120\sqrt{2}=169.71V$