Why convert impedances to the same per-unit base?

Why convert impedances to the same per-unit base?

• A. To normalize impedances to a common base for consistent comparisons and summation.
• B. To change actual impedance values.
• C. To convert impedance into voltage.
• D. To make numbers larger for readability.

Answer: (A)

The main idea here is normalization: expressing all impedances on a common reference so you can compare and combine them reliably. In a power system, different equipment and lines have different voltage and power ratings, so their actual impedances aren’t directly comparable or additive in calculations. By choosing a system base and turning each impedance into a per-unit value, Z_pu = Z_actual / Z_base with Z_base = V_base^2 / S_base, every impedance becomes a dimensionless quantity that shows how large it is relative to the system as a whole. Then you can sum impedances along a path or at a bus, and compare components across the network without worrying about mismatched bases. This normalization doesn’t change the real electrical behavior; it just makes calculations and visibility easier.

The main idea here is normalization: expressing all impedances on a common reference so you can compare and combine them reliably. In a power system, different equipment and lines have different voltage and power ratings, so their actual impedances aren’t directly comparable or additive in calculations. By choosing a system base and turning each impedance into a per-unit value, Z_pu = Z_actual / Z_base with Z_base = V_base^2 / S_base, every impedance becomes a dimensionless quantity that shows how large it is relative to the system as a whole. Then you can sum impedances along a path or at a bus, and compare components across the network without worrying about mismatched bases. This normalization doesn’t change the real electrical behavior; it just makes calculations and visibility easier.