Medium Voltage Application Guide

SWITCHGEAR
Transformer internal impedance, Z-int
The internal impedance is 0.28 .
Exercise
Calculate the transformer's output terminal voltage drop if the load was drawing 6000 A (I-load).
Internal voltage drop, U-int
U-int
I-load Z-int
1000
6000 0.28
1000
1680
1000
1.68 kV
The internal voltage drop is 1.68 kV.
Secondary output voltage due to
overload, U r'
r' E U-int
7.33 1.68
5.65 kV
The secondary output voltage is 5.65 kV.
Output voltage drop
U r U r'
The output voltage drop is 0.95 kV, or 14% U r
Page 146 Medium Voltage Application Guide 710-12280-00A