Unbalance & open-phase analysis
Voltage unbalance degree (negative / zero sequence), neutral-point displacement, and after an open conductor: the per-phase voltage distribution and the continue-to-supply verdict.
This column needs a scheme before it can calculate
Every study here (load flow, short circuit, harmonics, cables…) runs the real engine on real engineering data, so a scheme has to exist first. There is none yet — so instead of an empty page, here is how to start.
10 kV incoming (200 MVA short-circuit level) → 1250 kVA transformer (Dyn11) → LV main switchboard → busbar → 5 feeders plus a fire/emergency ATS branch. 1000 kW calculated load, cosφ 0.85, power-factor target 0.95.
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Definitions, units and why the number matters for selection and quotation. Searchable, grouped by topic, collapsed by default.
Every ? mark on this page opens the same explanation in place — no page change.
4 term(s) shown of 4
Per-unit bus voltage in a load-flow result: the node voltage divided by its base voltage, so 1.00 pu is nominal.
Why it matters: It is the acceptance number of every voltage-drop check (commonly 0.95–1.05 pu). A node below the band means equipment malfunction and a grid-code breach, and the answer is a larger cable, a different transformer tap or a compensation device — a quotation change, not a note.
Voltage unbalance: how far a three-phase voltage set departs from symmetry, expressed as the ratio of the negative-sequence (or zero-sequence) component to the positive-sequence component.
Why it matters: Motors and converters derate and overheat on unbalanced supply — limits are set by standard or by the machine vendor (for reference: IEC 61000-2-2 gives 2 % for LV networks), so the applicable limit must be named. Reducing it usually means redistributing single-phase loads or resizing the neutral.
Per-unit value: a quantity expressed as a fraction of a chosen base value (1.00 pu = nominal voltage or rated power), the standard language of power-system studies.
Why it matters: It lets a 0.4 kV LV board and a 110 kV network be compared on one axis and one chart. Voltage 0.95–1.05 pu is the usual acceptance band, so any per-unit figure in a report can be read directly against the criterion.
Loading: the current (or power) carried by a branch expressed as a percentage of its rated capacity.
Why it matters: It is the acceptance number for cables and transformers. Above 100 % the element will trip or have to be derated, and the margin left at the design case is exactly what the customer is paying for — so it must be shown with the assumption (load factor, ambient temperature) that produced it.