The plant and the line
Arrows: the current flowing into the fault from each end. 3I0: the current returning through a grounded neutral.
Fault current along the line
The fault is at the generator terminals, off this line. Move the distance slider to put it back on the line.
Zero sequence in the transformer
Line side and generator side
Thick arrows are phase currents. Thin arrows are sequence pieces: solid = positive, dashed = negative.
Currents at each end
Phase currents flowing into the line at each end, toward the fault.
Show the networks: both sides of the fault
Each sequence network seen from the fault point F: the plant side on the left, the far end on the right. Pills are the currents each side sends to F (pu).
How each connection treats zero sequence
| Transformer | Seen from the line | Seen from the generator |
|---|
A far-end Yg–Δ transformer (grounded wye toward the line) is a shunt to ground for zero sequence: it feeds pure zero sequence into a ground fault.
Assumes the transformer's zero-sequence reactance equals its leakage reactance (shell-form or five-limb core). A three-limb core-type Yg–Yg has a low zero-sequence magnetizing impedance and behaves partly like a delta.
Numbers
| Where | pu | Amps |
|---|
Generator side first. Δ = delta, Yg = grounded wye, Y = wye.
With no transformer the generator terminals are bus S, at the start of the line.