C. Per-unit system
Base selection, per-unit conversion, per-unit transformers, power-system normalisation.
Lessons
Lesson 1
Per-unit system + base conversion
Why expressing every quantity as a fraction of a base makes power-system math beautiful — and how to convert between bases without panic.
Lesson 2
Per-unit analysis in transformers
Nameplate %Z, base conversion to system MVA, the single-impedance equivalent, parallel-operation load sharing, auto-transformer kVA saving, and SLG-fault calculation through a Δ-Y_n transformer.