Question

A generator of negligible resistance having 1 p.u. voltage behind transient reactance is subjected to different types of faults when its neutral is solidly grounded.

Type of fault Resulting fault current in p.u.
L - L 2 p.u
L- G 3 p.u.

Then the value of zero sequence reactance (in p.u) is _________

• A. 0.134

Answer 1

The correct option is A 0.134
Line to line fault current, $\left|I_f\right|=\frac{\sqrt{3}.E_a}{X_1+X_2}$

$\left|I_f\right|=\frac{\sqrt{3}}{X_1+X_2}$

$2=\frac{\sqrt{3}}{X_1+X_2}$

$X_1+X_2=\frac{\sqrt{3}}{2}p.u.$

Line to ground fault current $=\frac{3.E_a}{X_1+X_2+X_0}$

$3=\frac{3}{X_1+X_2+X_0}$

$\therefore X_1+X_2+X_0=1$

$X_0=1-(X_1+X_2$)

$X_0=1-\frac{\sqrt{3}}{2}$

Zero sequence reactance, $X_0=0.134p.u.$