Protection Engineering Basics and Schemes Protection Engineering | Page 96

U n is nominal voltage, We can also use V for voltage Z SC is equivalent short circuit impedance of circuit Three phase Short circuit current( I 3∅SC)

Can be calculated as

I 3∅SC =

U n( √3) Z SC

In medium and high voltage network, as per IEC standard 60909,

I 3∅SC =

1. 1U n( √3) Z SC

Impedances: In Transformers,

Z =( V SC %/ 100) ∗( V n / S n)

Where, V SC is short circuit voltage, provided by manufacturer in %

pg. 96