Definition
A normalization technique in which all power system quantities — voltages, currents, impedances, and powers — are expressed as dimensionless fractions of defined base values (typically base MVA and base kV). The per-unit system eliminates the complexity of transformer turns ratios from network equations, makes cross-voltage-level comparisons straightforward, and results in most machine and transformer impedances falling in a narrow, intuitive range (0.05 to 0.20 pu). All major power flow, stability, and fault analysis software operates in per-unit; engineers must convert base values when connecting equipment rated on different voltage or MVA bases.
Topic Deck
Electrical Engineering Fundamentals
Source
FERC Pro Forma OATT / LGIP