Question

What will the zero-sequence current when line to ground fault occurs and the current in faulted phase is 300 A?
1. 100 A
2. 300 A
3. 50 A
4. 150 A

Answer 1

Correct Answer - Option 1 : 100 A

Zero sequence current in LG fault
For LG fault, all the sequence currents are equal.

\({I_{R0}} = \frac{{{I_f}}}{3} = \frac{{300}}{3} = 100\;A\)

Where
IR0 is the zero-sequence current
if is the fault current

Type of fault	Percentage of occurrence	Zero sequence current
L-G	70 – 80%	Ia0 ≠ 0
L-L	15 – 20%	Ia0 = 0
L-L-G	10%	Ia0 ≠ 0
L-L-L	<1%	Ia0 = 0
L-L-L-G	2 – 3%	Ia0 ≠ 0

 

The type of fault that includes ground has zero-sequence current.

Like L-G, L-L-G, L-L-L-G

Importance of Zero sequence current: 

In case of Ground faults like LG, LLG the fault current pass through the ground to the neutral and providing a relay between the neutral and ground, the zero sequence currents are passing through this relay for protection of electrical equipment like generator, transformer etc and the relay is called earth fault relay or ground fault relay.