Protection Engineering Basics and Schemes Protection Engineering | Page 212
I restraint min = 1.96A Considering errors, we select
Our I diff min and I diff max is 0.098A, which means our setting will not be less then 0.098A, after considering multiple errors and margins we selected nearest 0.2A as our I diff > setting.
Calculation of I diff ≫:
We have 33 / 11KV Transformer of 20MVA rating with % Z of 12.50
MVA short = MVA % Z
= 20 12.50 ∗ 100
MVA short = 160MVA
since as calculated, I SCHT = 2799.356A and I SCL = 8033A
Normally high set or I diff ≫ will be 1.3 times of HT fault current