Transformer Voltage Regulation from %R and %X

VR% = load x (%R cos + %X sin) + load^2 x (%X cos - %R sin)^2 / 200. The nameplate %Z alone does not give it -- the drop depends on the %R / %X split and the load power factor. With %R 1.2, %X 5.0 at 0.85 lagging, full load, the secondary sags +3.72% from no-load to full-load; make the same 0.85 power factor LEADING (a PV-exporting or over-corrected bus) and the voltage RISES -1.50% above nominal, tripping over-voltage relays. Returns the signed regulation so both the sag and the rise are visible -- the number the tap changer is set from. Terminal regulation, not the feeder drop; the utility's voltage study governs.

cos = pf; sin = sqrt(1 - pf^2) x (leading ? -1 : +1); VR% = load x (%R cos + %X sin) + load^2 x (%X cos - %R sin)^2 / 200.

Transformer voltage-regulation approximation from %R, %X, and load power factor (an IEEE C57 test-report quantity), first-principles; the utility's voltage study governs the actual profile.

The regulation from %R, %X, and power factor is a standard first-principles approximation; %R and %X come from the transformer's IEEE C57 test report.

Estimate. AHJ and licensed professional govern.

Field names used by the API: percent_r, percent_x, power_factor, leading, load_fraction, vr_percent

• Impedance split regulation uses %R and %X separately, not just %Z; %Z = sqrt(%R^2 + %X^2)IEEE C57 test report
• Power-factor sign lagging sin positive (voltage sags), leading sin negative (voltage can rise)load power factor
• Scope terminal regulation only; conductor voltage drop adds on topscope of this tile