Question

A three phase bridge rectifier is supplied from a Y-connected 208 V, 60 Hz supply. The average load current is 60 A and has negligible ripple. If the line inductance per phase is 0.5 mH, then the percentage reduction of output due to commutation is _________%.

• A. 3.84

Answer 1

The correct option is A 3.84
Average output voltage of a three phase diode bridge rectifier is,
$V_0=\frac{3V_{mL}}{\pi }$
$=\frac{3\times \sqrt{2}\times 208}{\pi }=280.89V$
The reduction of voltage due to source inductance,
$V_x=\frac{3\omega L_s{I}_0}{\pi }=\frac{3\times 2\pi \times 60\times 0.5\times {10}^{-3}\times 60}{\pi }$
$\therefore$ percentage reduction of output voltage due to source inductance
$=\frac{10.8}{280.89}\times 100=3.84\%$