Editing Per-unit system (section)

==Purpose==

There are several reasons for using a per-unit system:
* Similar apparatus (generators, transformers, lines) will have similar per-unit impedances and losses expressed on their own rating, regardless of their absolute size. Because of this, per-unit data can be checked rapidly for gross errors. A per unit value out of normal range is worth looking into for potential errors.
* Manufacturers usually specify the impedance of apparatus in per unit values. 
* Use of the constant <math>\textstyle \sqrt{3} </math> is reduced in three-phase calculations. 
* Per-unit quantities are the same on either side of a transformer, independent of voltage level
* By normalizing quantities to a common base, both hand and automatic calculations are simplified. 
* It improves numerical stability of automatic calculation methods.
* Per unit data representation yields important information about relative magnitudes.
The per-unit system was developed to make manual analysis of power systems easier.  Although power-system analysis is now done by computer, results are often expressed as per-unit values on a convenient system-wide base.