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Percentage Resistance and Reactance

9.12. Percentage Resistance and Reactance 

The important advantage of expressing resistance and reactance of a transformer in percentage is that the percentage resistance and percentage reactance have same values whether determined referred to primary or secondary whereas when expressed in ohms they have different values when referred to primary and secondary.

Further, percent reactance and impedances are convenient for computing the current that will flow in a transformer when the secondary is accidentally shorted. When the secondary is shorted

Unless the transformer is quite small, equivalent resistance is negligible and percent reactance may be substituted for percent impedance in the above equation (iv).

  • Another method of designating the resistances and reactances is by the per unit values. The per unit values are equal to the percentage values divided by 100.¬†