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The following sequence currents were recorded in a power system under a fault condition IтВЪтВТтВЫс╡втВЬс╡вс╡етВС = j1.923 pu, IтВЩтВСgтВРтВЬс╡вс╡етВС = тАУ j0.8 pu, IzтВСс╡гтВТ = тАУ j1.246 pu.The fault is
Line to ground
Line to line
Line to line to ground
Three-phase
Line to line to ground
{"type":"reasoning","methodBadge":"Symmetrical Components Analysis","trick":"For a fault to be Double Line to Ground (LLG), all three sequence components (positive, negative, and zero) must be non-zero and present, unlike LG (all equal) or LL (zer...
For a fault to be Double Line to Ground (LLG), all three sequence components (positive, negative, and zero) must be non-zero and present, unlike LG (all equal) or LL (zero sequence is zero).
Check sequence presence
Observe that Ipositive = j1.923, Inegative = -j0.8, and Izero = -j1.246. Since all three components are non-zero, the fault must involve the ground and at least two lines.
Evaluate fault constraints
In an LG fault, Ipositive = Inegative = Izero. In an LL fault, Izero = 0 and Ipositive = -Inegative. Since none of these conditions are met, it satisfies the criteria for an LLG fault.
C is correct because the presence of all three non-zero sequence components is the unique signature of an unsymmetrical double line-to-ground fault.
Always remember: If zero-sequence current is zero, the fault is either LL or 3-phase. If zero-sequence is non-zero, it must involve the ground.