One transformer,
taken module by module.

A liquid-immersed distribution transformer of a size you meet on almost every commercial and industrial site. The 433 V secondary is the Australian no-load convention — see the note on why.

The idea behind the calculator is that a transformer is one object. You enter it once — rating, voltages, vector group, impedance, losses — and six modules each compute a different view of that same object, the way a protection engineer, a cable designer and a compliance reviewer each ask the nameplate a different question. Here is the full set for the unit above.

Full-load current is the anchor every other module hangs off. At 11 kV the primary draws 52.49 A; the 433 V secondary carries 1333.4 A. Read the same unit at 400 V instead and the secondary rises to about 1443 A — a ~8% swing that flows straight into busbar and cable sizing, which is exactly why the secondary voltage is a deliberate input, not a default. The Dyn11 group fixes the LV as a solidly-earthable star leading the HV delta by 30° — the clock number matters the moment two transformers are paralleled or a damage curve is laid onto a grading study.

With an infinite source the three-phase fault is set by the transformer's own impedance: 26.67 kA at the 433 V terminals. Asymmetry is where the X/R earns its place — at a combined X/R of 6 the IEC κ-factor is 1.614, pushing the first-cycle peak to 60.88 kA. That peak, not the RMS, is what a device's making capacity has to survive.

Regulation is the volt-drop the load never sees on a no-load test. At 0.8 lagging the 5% impedance resolves to a 3.67% drop, so the 433 V no-load secondary sits near 417 V at full load — before the LV network takes its own share. This is the whole reason the unit is wound for 433 rather than 400: the regulation is spent on purpose, so the customer end still lands inside the statutory band.

Australia checks distribution transformers at half load, where the fixed iron loss and the current-dependent copper loss trade places — for this unit efficiency peaks near there at 99.31%. GEMS minimum-efficiency verification is the calculator's headline: no international transformer tool does Australian MEPS checking.

Given a 433 V target the nominal tap lands exactly on it, so nothing needs moving. Change the target — pin 415 V for a New Zealand site, or a specific measured upstream voltage — and the module recommends the tap whose no-load secondary comes closest, and shows the full-load current shift that rides with the change. Taps are the one field decision the nameplate leaves open, and the calculator closes it against a number you choose rather than a house default.

A 1000 kVA three-phase unit sits in Category II of IEEE C57.109, whose through-fault curve carries both a thermal limit and — for frequently-faulted service — a mechanical limit at the high-current end. The module produces the withstand curve ready to drop straight onto the Protection Coordination chart against the existing device library: a transformer damage curve is only useful next to the relays that are meant to clear before it.

Everything cited, everything disclosed

The report that comes out of this carries all six modules, the citations behind each — IEEE C57.12.00, IEC 60909-0:2016, AS 60076.1, the GEMS determination and IEEE C57.109 — and an assumptions register naming every engine-supplied default it leaned on: the Z₀ / Z₁ ratio, the cooling-uprate factor, the load-loss reference temperature and the inrush multiplier. Nothing is a hidden constant.

Every figure on this page was produced by the Ampacities Transformer engine for the nameplate stated, at its default assumptions (Z₀/Z₁ ≈ 0.9, 0.8 lagging power factor for regulation). Enter the same unit to reproduce them and export the signed report. Figures are engineering estimates for the stated inputs, not a substitute for manufacturer test certificates.