Reclose study — fault → protection clear → reclose
Three quasi-steady operating stages (fault, protection clearing, reclosure). Each stage runs the real load-flow solver, and the fault stage runs the real short-circuit engine. Both branches of the reclosure — a transient fault (reclose succeeds) and a permanent fault (reclose fails and trips again) — are checked for branch overload and bus voltage violations.
This page 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 must exist first. There is none yet — so instead of an empty page, here is how to start.
GRID-10kV → 1250 kVA transformer → LV bus → 600 kW load + 300 kvar PFC. Loaded in one click; replace the data with yours at any time.
Load the example and continue →In the studio: place devices, wire them, pick models — that becomes your project scheme (exportable drawings / BOM / report).
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.
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
Initial symmetrical short-circuit current at the fault point (IEC 60909-0): the rms current the network drives into a bolted three-phase fault, with the voltage source replaced by the c·Un/√3 equivalent.
Why it matters: It is the number every device rating is compared with — Icw, breaking capacity and the cable thermal check all read against Ik. Under-estimate Ik and the panel you quote will be destroyed on the first fault; over-estimate it and the client pays for switchgear he does not need.
Ratio of the equivalent reactance to the equivalent resistance seen from the fault point (IEC 60909-0).
Why it matters: It fixes two things at once: the peak factor κ (hence ip) and the decay rate of the DC component. A high X/R (inductive LV feeds, generator sources) gives both a higher peak and a longer DC transient, which the breaker must interrupt.
Aperiodic (DC) component of the short-circuit current, i_dc = √2·I″k·e^(−ωt·R/X) (IEC 60909-0): the decaying offset that rides on top of the symmetrical component.
Why it matters: It is the extra current the breaker has contact to interrupt at the moment of contact parting, and it is why the required breaking capacity is higher than I″k for fast (generator-close) faults. In a quotation it appears as the rated breaking capacity at that % DC component.
Protection clearing time: the total time from fault inception to arc extinction — relay detection + intentional delay + breaker operating time.
Why it matters: In an arc-flash study the incident energy is almost proportional to the clearing time, and the PPE category is selected from it. Halving the clearing time usually halves the energy and can drop the required PPE by one step — which is a direct operating-cost item.
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.
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.
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.