Question

For a bolted three-phase-to-ground fault, sequence-fault currents ________ are zero, sequence fault voltages are ______, and line-to-ground voltages are ________.

Short answer

The correct answers for the blank are _{$l_0$and}$l_1$, zero and zero .

Step-by-step solution

Definition of three-phase fault.

A bolted three-phase fault defined as the situation when three conductors are connecting together with zero phase impedance between them. Where, in a balanced three phase symmetrical system the fault current magnitude is balanced equally.

Determine the complete sentence.

Consider $l_0$is a zero sequence fault current, $l_1$is positive sequence fault

current and $l_2$is negative sequence fault current.

Consider $V_0$is zero sequence fault voltages, $V_1$is positive sequence fault voltage and $V_2$is negative sequence fault voltage.

Consider $V_{ag}$is line to ground voltage at phase, $V_{bg}$is line to ground voltage at phase b and $V_{cg}$is line to ground voltage at phase.

Assume$V_F$is fault voltage regarding a bolted three phase fault.

Determine the sequence component of line to ground voltages at the fault terminals.

..............1

Here,$Z_0,Z_1$and $Z_2$are Thévenin equivalent reactance and , $l_0,l_1$and $l_2$are sequence fault currents.

Determine bolted three phase fault, the sequence fault currents are

$l_0=l_{}=0$

And $l_1=\frac{V_F}{Z_1}$

From equation (1), the sequence fault voltages are

$V_0=V_1$

=$V_2$

=0

Since, lines to ground voltage are

Therefore, for a bolted three phase to ground fault sequence fault currents $l_0$and $l_1$are zero sequence fault voltages are zero and line to ground voltages are zero..