CT Sizing Claculation

CT sizing calculations Details CT accuracy chosen

CT Burden CTR chosen CT Primary CT secondery Max Fault current Fault current in CT sec Relay Burden Relay resistance = Rr = Sr/Isec*Isec) Conductor Cross section No. of runs Conductor resistance @ 70 Deg = Rl Length of Conductor Bet CT & relay Two way lead resistance Calculation of Vk required CT secondery resistance

Vk reqd = If If (sec)x ( Rct+2RL+Rr) Vk available= Is Vk req > Vk avai Conclusion - CTR rating

Note -Data to be entered in the field

5 P 20 15 8 0 0/ 1 I pri I sec If If sec Sr Rr

RL L 2 RL

Rct Vk req Vk avai

Value 20

Unit

15 80 0 80 0 1 40 0 00 50.00 0 .2 5 0 .2 5 2.5 1 8 .8 7 20 0 .3 5

VA

5 .0 0 2 8 0 .2 4 30 0 Yes OK

Ohm volts volts

Amp Amp Amp Amp VA Ohm Sq mm Ohm/km meter Ohm