Protection Engineering Basics and Schemes Protection Engineering | Page 135
I Primary Short circuit Current = I PSC 1000
= MVA SC ∗
1.732 ∗ V Primary
5.3.5 One Case Study( Protection Relay-OC-Setting)
We need to set overcurrent( non-directional) and earth fault pick up values for 500KVA transformer( Dyn11) with % Z = 4.75, 11 / 0.433 KV auxiliary transformer feeder.
MVA short = MVA sc = 10.52632MVA MVA
I primary full load = I PFL =
1.732 ∗ V primary 1000
I PFL = 0.5 ∗
1.732 ∗ 11 I PFL = 26. 24A
I Primary Short circuit Current = I PSC 1000
= MVA SC ∗
1.732 ∗ V Primary
1000 = 10.52632 ∗
1.732 ∗ 11 I PSC = 552. 5A
I secondary full load = I SFL = 0.5 ∗ I SFL = 666. 7A