N-1 transfer & storage SOC
Two questions on one page. (1) N-1: for every fault case, can the load still be picked up by closing a tie switch — and which branches are overloaded or which bus voltages fall out of band after the transfer? (2) Storage: what does the state of charge do over 24 hours — charge/discharge power, and whether the SOC window is violated (over-charge / over-discharge)? Every number comes from the engine; the load flow is re-solved for real for each transfer candidate.
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.
Load the real example scheme and start calculating →The scheme and its parameters go straight into your browser; replace the data with your own at any time.
Calculator mode computes the few outputs that only depend on parameters you type in yourself. Anything that genuinely needs the whole system (full-network load flow, coupling with other devices) is shown as “needs a scheme” and no number is given.
Calculator mode is not available for this column yet — use one of the ways below.
Nothing is pre-filled and nothing is invented: leave a required field empty and the result area says “unavailable”.
In the studio, place devices, wire them and pick models — that becomes your project scheme (drawings / BOM / report can be exported).
Open the studio →Use the chat bubble bottom-right, or Contact us — we will set the example to your site parameters.
Note: every number comes from the engine. With no scheme, nothing is invented here.
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.
8 term(s) shown of 8
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.
State of charge of a battery or BESS: the remaining energy as a percentage of the rated (or usable) capacity.
Why it matters: It bounds what the storage can deliver at any instant, so it drives the protection settings, the dispatch strategy and the delivered-energy guarantee. A quoted availability figure is meaningless unless the SOC window it assumes is stated.
Depth of discharge: the complement of the state of charge — how much of the capacity is cycled out, normally quoted as a maximum in cycle-life specifications.
Why it matters: It is the trade between usable capacity and battery life: the same nominal kWh quoted at 80 % DOD delivers fewer cycles than one quoted at 60 %. Because it changes both the usable kWh and the replacement date, the DOD must be on the datasheet next to the price.
Round-trip efficiency of a storage system: the energy returned during discharge divided by the energy absorbed during charge over a complete cycle.
Why it matters: It decides how much of the energy you pay for actually comes back out, and therefore the real cost per delivered kWh. Watch the boundary of the figure (DC-DC looks much better than AC-AC) — comparing two offers on different boundaries is a common source of wrong quotations.
Capacity factor: the energy actually produced over a period divided by the energy the plant would have produced running at its rated power for the whole period (for PV this is dominated by irradiance and temperature, not by the inverter).
Why it matters: It is the number that converts a nameplate kWp into annual kWh, and therefore into revenue and payback. A quotation that gives only the kWp figure does not say what the plant will actually deliver — ask for the assumed capacity factor.
N-1 (single-contingency) criterion: the network must remain within its operating limits with any one single element (line, transformer, generator) out of service.
Why it matters: It decides how much redundancy — parallel feeders, duplicated transformers, busbar sections — goes into the quotation. If it is not stated explicitly, the design tends to be single-radial and the customer finds out during commissioning.
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.
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.