ADVANTAGES OF PER UNIT SYSTEM

PER UNIT SYSTEM

ADVANTAGES OF PER UNIT SYSTEM

1. While performing calculations, referring quantities from one side of the transformer to the other side serious errors may be committed. This can be avoided by using per unit system.
2. Voltages, currents and impedances expressed in per unit do not change when they are referred from one side of transformer to the other side. This is a great advantage.
3. Per unit impedances of electrical equipment of similar type usually lie within a narrow range, when the equipment ratings are used as base values.
4. Transformer connections do not affect the per unit values.
5. Manufacturers usually specify the impedances of machines and transformers in per unit or percent of name plate ratings.
6. Transformers can be replaced by their equivalent series impedances.
7. Equipment impedances can be easily estimated since their per unit impedances lie within a relatively narrow range.
8. Reduced calculations in three-phase systems.
9. By the choice of voltage bases, the solution of networks
   containing several transformers is easy.
10. More usefully for digital computation.
11. For apparatus of the same general type the p.u. and volt
    drops or losses are in the same order, regardless of size.
12. For transformers the p.u. of impedances are same for
    primary and secondary sides.

PER UNIT CONVERSION PROCEDURE OF SINGLE PHASE