Question

A sustained $3-\varphi$ fault occurs in the power system as shown below and corresponding current and voltage phasors during the fault ( on a common reference) are also shown after natural transients. The location of fault in the system is at location

• A. A
• B. C
• C. D
• D. B

Answer 1

The correct option is D B

During fault, the current value increases, the voltage drop and power factor decreases, reactive power drawn increases generally due to reactance of line.
$\therefore$ Fault current is high having 90° lagging nature in a transmission line for phasor diagram.
The phasor of ${\overrightarrow{I}}_2$ is having largest magnitude and lags voltage ${\overrightarrow{V}}_1$ by almost 90°.
So quantities ${\overrightarrow{V}}_1$ and ${\overrightarrow{I}}_2$ resembles faulty condition.
$\therefore$ location B is most feasible fault position according to phasor diagram.