Protection Engineering Basics and Schemes Protection Engineering | Page 223

For tripping, situation is I diff > KI restraint

Let suppose our slope is 40 % then,

I diff > 0.4 ∗

1. 363637 + 0. 787319 2

For high set; I diff ≫

I diff > 0.430191A

I primary = 2361.957A

We set it between 8-12 times, as inrush current is approximately 8-12 times of full load current or minimum 1.3times of fault current.

I inrush = 28343.48A

As we install CT at primary side of 3000:1, the at secondary of CT I inrush is 9.4478A

We set I diff ≫ 10A

pg. 223