Short Circuit Calculation

[roshan1430]

I am trying to calculate short circuit contribution of a 12.4/2.4kv transformer(z=6.3%) . The transformer comes with four kVA ratings 3750/4200/4688/5250 (KNAN/KNAF, 55C/65C). What kVA rating should I use for SC calcs.
Thanks you

 

[Ingenieur]

the nameplate should tell you which one the pu z is associated with
usually the non fan lower temp rating 3750

once you calc z in ohms the i fault is the same for all kva's

assume pu z is at 3750 kva base
X base = v^2/S = 1.536
1 ph z = 0.063 x 1.536 = 0.0968 Ohm
3 ph z = 0.1676 Ohm

so a i sc l-l = 2400/0.1676 = 14319 A
only depends on z act (at the rated base S) and v
assuming infinite bus

 

[roshan1430]

Thank you so much. Checked with manufacturer, impedance rating was for 3750. Thanks lot.

the nameplate should tell you which one the pu z is associated with
usually the non fan lower temp rating 3750

once you calc z in ohms the i fault is the same for all kva's

assume pu z is at 3750 kva base
X base = v^2/S = 1.536
1 ph z = 0.063 x 1.536 = 0.0968 Ohm
3 ph z = 0.1676 Ohm

so a i sc l-l = 2400/0.1676 = 14319 A
only depends on z act (at the rated base S) and v
assuming infinite bus