The bus and its neutral
Dotted: the ground return. Press the meter to read it.
Voltages to ground
Picture
Where the fault current returns
Intermittent-arc overvoltages are not modelled. They are the reason for the IR ≥ IC rule.
What ground current buys, and what it costs
More ground current buys
…and costs
Zero network
Numbers
| Quantity | pu | Real units |
|---|
In the voltage triangle, ground sits at g = −V0 = z0·E ÷ (z0 + z1 + z2 + 3Rf) from the centre: an arc from the centre (Rf → ∞) to the faulted corner (Rf = 0). It is a semicircle only when the zero path is purely capacitive.
Why generator neutrals use high resistance
Generator neutrals are usually grounded through a high resistance. A generator's own X0 is tiny, so solid grounding would make its ground faults the largest of all (chapter 3 shows the line-to-ground fault growing as X0 falls). Its step-up transformer's delta also keeps the line's ground faults away from it (chapter 5 shows why).
Neutral
Fault on phase