pereenheidsparameters

Pereenheidsparameters, or per-unit parameters, are dimensionless quantities obtained by normalizing electrical quantities against chosen base values. They are widely used in electrical power engineering to simplify calculations and comparisons across equipment and network segments that operate at different voltage levels and ratings. In a per-unit system, voltages, currents, impedances, and powers are expressed as fractions of their respective bases, making the operating point appear near unity (about 1 p.u.) for typical equipment.

Base quantities are selected for the system: V_base, I_base, S_base (apparent power). From these, Z_base = V_base^2 / S_base and Y_base = S_base / V_base^2. The per-unit value is obtained by dividing the actual quantity by its base: V_pu = V_actual / V_base, I_pu = I_actual / I_base, Z_pu = Z_actual / Z_base, S_pu = S_actual / S_base, Y_pu = Y_actual / Y_base.

Common practice is to set S_base to a standard value (often 100 MVA) and to choose V_base to match the nominal system voltages. Then I_base follows as S_base / V_base and Z_base follows from V_base^2 / S_base. When multiple voltage levels exist, impedances are often referred (converted) to a common base using turns ratios of transformers.

Applications and advantages: per-unit quantities simplify the modeling of power systems, especially in load-flow, short-circuit, and transient stability studies. They reduce numerical range, enable direct comparison of equipment, and reduce the impact of differing units during calculations.

Limitations: the results depend on the chosen bases; converting between bases requires careful handling of transformer off-nominal taps and network topology. Nonlinear device behavior may reduce the intuitive meaning of p.u. values in some operating regions.