Protection Engineering Basics and Schemes Protection Engineering | Page 138

At 200 / 1, I e >= Pick up earth =

10. 496

200 1

= 0. 05248A

I PSC

PSM =

40 % of I PFL 552.5

= = 52. 639A

40 % of 26.24 0.14 t = TMS ∗

I 0. 02 − 1 0.14

0.6 = TMS ∗

52.639 0. 02 − 1

TMS = 0.35355Sec Instantaneous setting for earth fault will be 5 times of PSM I e ≫ = 5 ∗ 52.639 I e ≫ = 263.1955A

CT Ratio is 200 / 1,

I e ≫ =

263. 1955

200 1

= 1. 315978A

Tripping nature of I e ≫ is definite minimum time

pg. 138