Transformer Full-Load Current

Method, example and boundaries

For one winding, I = S / (k × V). Single-phase uses k = 1 and the voltage between that winding’s terminals. Balanced three-phase uses k = √3 and line-to-line voltage. S is rated apparent power in volt-amperes. A 630 kVA winding at 400 V three-phase is 630000 / (√3 × 400) = 909.326… A, shown as 909.33 A. A 100 kVA winding at 380 V three-phase is 151.93 A. Ten kVA at 220 V single-phase is 10000 / 220 = 45.45 A.

Primary and secondary are the same formula with different voltages, so this page replaces separate primary-current and secondary-current titles. Enter only the winding you want. Power factor, load factor, inrush, and tap position are not applied. The result is not a breaker, fuse, cable, or protection setting.

Source: Schneider Electric Electrical Installation Guide, Choice of transformer rating (SRC-065). That page writes In = Pa × 10³ / (U√3) for three-phase and In = Pa × 10³ / V for single-phase. Its table uses no-load voltages of 237 V and 410 V and rounded amperes; those rounded values are not copied here. The shortcut “kVA × 1.4” is not used. IEC 60076 is named on that page; a clause number was not checked and is UNVERIFIED. GB full-load-current clause numbers are UNVERIFIED. Voltage presets only fill 220/380 V, 230/400 V, or 120/240 V from the existing site profiles.