[freak16]

The normal method
of  expressing  transformer  impedance  is  as  a  percentage  voltage  drop  in  the
transformer at full-load current and this reflects the way in which it is seen by
system designers. For example, an impedance of 10% means that the voltage
drop at full-load current is 10% of the open-circuit voltage, or, alternatively,
neglecting any other impedance in the system, at 10 times full-load current, the
voltage drop in the transformer is equal to the total system voltage.

Formula written by MH is perfect.

Thenormalmethod
ofexpressingtransformerimpedanceisasapercentagevoltagedropinthe
transformeratfull-loadcurrentandthisreflectsthewayinwhichitisseenby
systemdesigners.Forexample,animpedanceof10%meansthatthevoltage
dropatfull-loadcurrentis10%oftheopen-circuitvoltage,or,alternatively,
neglectinganyotherimpedanceinthesystem,at10timesfull-loadcurrent,the
voltagedropinthetransformerisequaltothetotalsystemvoltage.Expressed
insymbolsthisis:
Vz %Z
IFLZ
E
100

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