Relay Setting Calculation

PSM=14000/2300=6.086 Actual operating time=3.806*0.18= 685 ms E/F setting: 20%, 0.3

Actual operating time= 2.26*0.3=678 ms Stand by E/F: 20%, 0.55 Actual operating time=2.26*0.55=1243 ms Bus-zone setting: 0.2,200 ohm

Fault current=14000 amp B/Z CTR=800/1 Rct (Max) =2.3 ohm Vk (Min) =242 V Sec Fault current=14000/800=17.5 A Voltage across CT=17.5*2.3=40.25 V If current setting =0.2, Rstab=200 ohm HVREF setting: 0.75A, 35 ohm Fault current at 33 kV side = (14000*6/33) =2545 amp

CTR=400/5 Rct (max) =0.55 ohm Vk (min) =133 volt Vk/2=65 volt Sec current=2545 *5/400=31.8 amp Voltage across CT=31.8*0.55=17.49 volt If relay setting =0.75 amp Rstab=35 ohm Voltage across CT=23 volt

LVREF setting: 1A, 50 OHM

Fault current at 6kv side=14000 amp CTR=2000/5 Rct (max) =0.925 ohm Vk (min) =293 volt Sec ct=14000*5/2000=35 amp Voltage across CT=35*0.925=32volt If current setting=1 amp Rstab=50 ohm Voltage across CT during fault=50*1=50 volt