Relay setting CalculationBase MVA=100Fault MVA=1200Source impedance=0.083Cable impedance=.015*4=0.06 ohmTransformer impedance=11 % at 20 MVA base=0.11*100/20=0.55 ohmTotal fault impedance at 6 kV Bus=0.083+.06+.55=0.693 ohmFault MVA= 100 MVA/0.693=145 MVA=150 MVA (approx)3 phase fault current at 6 kV bus=150/1.732*6 =14 KAOutgoing Feeders setting: 100%, 0.1, CT Ratio=800/5PSM=14000/800=17.5Relay opt time based on Std Curve= 0.014/[(PSM)0.02-1] = 2.37Operating time =2.37*0.1=0.237 s=237ms E/F setting: 20%, 0.1PSM=14000/160=87.5=20(max)Relay operating time on std formula=0.14/(20)0.02-1= 2.26Actual operating time= 2.26*0.1=226msIncomer feeder setting: 115%, 0.25, CT Ratio=2000/5Full load current=1848 amp at 6kvConsidering 25% overloading, load current=2310 amp=2300amp (approx)PSM= 14000/2300=6.086Relay operating time based on std formula=0.14/(6.086)0.02-1=3.806Actual operating time=3.806*0.25=950 msE/F setting: 20%, 0.4PSM=14000/400=35=20 (max)Relay operating time based on std formula=2.26Actual operating time=2.26*0.4=906msBus Section Feeder: 115%, 0.18

PSM=14000/2300=6.086Actual operating time=3.806*0.18=685 msE/F setting: 20%, 0.3Actual operating time= 2.26*0.3=678 msStand by E/F: 20%, 0.55Actual operating time=2.26*0.55=1243msBus-zone setting: 0.2,200 ohmFault current=14000 ampB/Z CTR=800/1Rct (Max) =2.3 ohmVk (Min) =242 VSec Fault current=14000/800=17.5 AVoltage across CT=17.5*2.3=40.25 VIf current setting =0.2,Rstab=200 ohmHVREF setting: 0.75A, 35 ohmFault current at 33 kV side = (14000*6/33) =2545 ampCTR=400/5Rct (max) =0.55 ohmVk (min) =133 voltVk/2=65 voltSec current=2545 *5/400=31.8 ampVoltage across CT=31.8*0.55=17.49 voltIf relay setting =0.75 ampRstab=35 ohmVoltage across CT=23 volt

LVREF setting: 1A, 50 OHMFault current at 6kv side=14000 ampCTR=2000/5Rct (max) =0.925 ohmVk (min) =293 voltSec ct=14000*5/2000=35 ampVoltage across CT=35*0.925=32voltIf current setting=1 ampRstab=50 ohmVoltage across CT during fault=50*1=50 volt