Which statement correctly names the three symmetric sequence networks and their connection during a solid three-phase fault?

Which statement correctly names the three symmetric sequence networks and their connection during a solid three-phase fault?

• A. Positive-sequence network Z1, Negative-sequence network Z2, Zero-sequence network Z0; connected in series across the fault.
• B. Positive-sequence network Z1, Negative-sequence network Z2, Zero-sequence network Z0; connected in parallel to the fault.
• C. Only Z1 is used for a solid three-phase fault.
• D. Zero-sequence Z0 is the only network involved in the fault.

Answer: (A)

In a solid three-phase fault, the three symmetric-sequence networks line up in series at the fault point, so the fault current flows through all three connected in a loop. Each network captures a different aspect of how the system responds: the positive-sequence network represents the balanced, normal system behavior; the negative-sequence network accounts for unbalance created by the fault; and the zero-sequence network handles currents that return through the neutral/ground path. Because the fault ties all three phases together, the currents and voltages must satisfy the series path, giving the fault current as If = Vprefault / (Z1 + Z2 + Z0). This is why the series connection of Z1, Z2, and Z0 correctly describes the solid three-phase fault.

In a solid three-phase fault, the three symmetric-sequence networks line up in series at the fault point, so the fault current flows through all three connected in a loop. Each network captures a different aspect of how the system responds: the positive-sequence network represents the balanced, normal system behavior; the negative-sequence network accounts for unbalance created by the fault; and the zero-sequence network handles currents that return through the neutral/ground path. Because the fault ties all three phases together, the currents and voltages must satisfy the series path, giving the fault current as If = Vprefault / (Z1 + Z2 + Z0). This is why the series connection of Z1, Z2, and Z0 correctly describes the solid three-phase fault.