from __future__ import division
#Variable declaration:
Is = 5 #rated secondary current of C.T
CS = 1.25 #current setting
TSM = 0.6 #time setting multiplier
IF = 4000 #fault current(A)
CR = 400/5 #current ratio of CT
#Calculation:
Ipc = Is*CS #pick-up current(A)
If = IF*CR #Fault current in relay coil(A)
PSM = If/Ipc #plug setting multiplier
#Corresponding to the plug-setting multiplier of 8 given in fig.21.16,
#the time of operation is 3.5 seconds.
top = 3.5*TSM #Actual relay operating time(s)
#Result:
print "The relay operating time is",top,"seconds"