Analyze Sequence Currents

In an unsymmetrical fault, the fault current can be resolved into positive, negative, and zero sequence components. The zero sequence current $I_0$ is defined as the average of the phase currents: $I_0 = \frac{1}{3}(I_a + I_b + I_c)$.

$I_0 = \frac{1}{3}(I_a + I_b + I_c)$

Evaluate Fault Conditions

For a Line-to-Ground (L-G) fault, $I_b = I_c = 0$, so $I_0 = I_f / 3$. For a Double Line-to-Ground (D-L-G) fault, the presence of two faulted phases leads to a non-zero sum of phase currents, typically resulting in a specific relationship between $I_0$ and the sequence networks.

$I_0 = \frac{1}{3} I_f$

Conclusion

Given the options provided and the context of the question regarding zero sequence current behavior during ground faults, the condition described corresponds to a double line-to-ground fault.

$I_{zero\,sequence} \neq 0$