Question

Using thevenin equivalent circuit, determine the rms value of the voltage across the 100 ohm resistor after the switch is closed in the 3-phase circuit shown in figure

• A. 115.5

Answer 1

The correct option is A 115.5
$V_{Th}=V_{ph}=\frac{400}{\sqrt{3}}\simeq 231V$

Now, to find $Z_{Th}$, replacing all the independent voltage source by short circuit,

We have,


$\therefore Z_{Th}=300||300||300=100\Omega$

$\therefore$ Thevenin's equivalet circuit:



$\therefore$ Voltage across $100\Omega$ resistor

$=231\times \frac{100}{100+100}$ (voltage division rule)

$=\frac{231}{2}=115.5V$