Expressing system quantities as fractions of a defined base unit simplifies the analysis of power systems. This approach, frequently used with single-phase equivalents of three-phase systems, allows engineers to work with dimensionless values, facilitating direct comparisons across systems with different voltage and power levels. For example, a 500 MVA transformer might have an impedance of 0.10 expressed in this normalized form. This 0.10 value represents the fraction of base impedance, making it easier to compare with transformers of different ratings.
This normalized approach streamlines calculations involving complex power systems and provides a clearer understanding of system behavior during faults or other disturbances. Historically, it arose from the need to manage increasingly complex power networks and has become a standard practice in power system analysis. Its use has significantly enhanced the efficiency and accuracy of power system design, operation, and control.