Why does the presence of transformers in power system necessitate the introduction of per-unit system

Why presence of transformers in power system necessitates introduction of per-unit system?

Answer: Due to the presence of transformers in power systems, many power system problems become tedious to solve using electrical units. Because the transformer turns ratio changes the electrical quantities of voltage, current, and impedance differently while moving from one voltage side to another side i.e If transformer turns ratio is n, if one moves from the high-voltage side of the transformer to the low-voltage side, there is a change in voltage by 1/n, similarly the current changes by n, and the impedance changes by 1/n^2. Due to this reason introduction of per-unit system is necessary. The per-unit system uses dimensionless quantities and when properly applied it results in all transformer turns ratios to 1.

Also read: Top 10 Questions on Transformers

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