Answer / yashpal

plug setting is = 3.75 means pick up= 3.75 A.Relay
operating time will depends on the charecteristic of relay.
(invese,normal inverse).if the fault current is 8000A then
current in the sec will be 10 A which is three times of
3.75A(connected plug setting),now just watch the relay
charteristic written on relay u can get the time required
for relay operation.(ex- for inverse charecteristic relay
for 3 time current & tms = 1 ,timing is 6.25 sec,so for
our problem timing will be 6.25 * 0.15=0.9375 sec.

Answer / yvb

your PSM set for 3.75 means 3.75 times of your py.
current. if fault current is 3.75 times of 4000 i.e 3.75 x
4000 = 15000 A. your relay will operate in 0.15 sec.(
Primary Injection.)on Secondary we can say 5 x 3.75 =
18.75A flows through ur relay.
Now comming to ur case if fault current is 8000A ie. 2
times of 4000 or u can say 2 times of 5 A.
Then your relay will operate in 0.282 seconds.

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