Medium Voltage Application Guide

SWITCHGEAR
Exercise
Select the primary input fuses required to protect an 11 kV/400 VAC, 1000 kVA, 3-phase power transformer.
The range of I n(FUSE) is 97.5~106 A. Use 100 A/12 kV, E-rated primary fuses.
Capacitor banks
Two primary factors affect fuse ratings when used with capacitor banks:
the peak inrush current which flows when a capacitor bank is energised. This can be up to 100 times the
nominal current rating of the capacitor bank.
transient voltages produced during capacitor bank switching.
Individual 3-phase capacitor bank
I n (FUSE) = 2 x I_ CAP
U n (FUSE) = 2 x U_ CAP
Back-to-back 3-phase capacitor bank
I n (FUSE) = 3 x I_ CAP
U n (FUSE) = 2 x U_ CAP
Exercise
Select the protection fuse required for a 300 kVAr/7.2 kV individual 3-phase capacitor bank.
I_ CAP
n(FUSE)
I_ CAP
n(FUSE)
U_ CAP
Use 50 A/17.5 kV, general purpose fuses
710-12280-00A Medium Voltage Application Guide Page 107