how to claculate earth strip size for 1500kVA transformer
for neutral and body
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Answer Posted / chandan tripathy
As per IS 3043, Cross Section Area of Earthing Conductor
(A) =(If x√t) / K
Where:
t = Fault current Time (Second).
K = Material Constant.
Example: Calculate Cross Section Area of GI Earthing Conductor for System has 50KA Fault Current for 1 second. Corrosion will be 1.0 % Per Year and No of Year for Replacement is 20 Years.
Cross Section Area of Earthing Conductor (A) =(If x√t) / K
Here:
If = 50000 Amp
T = 1 Second
K = 80 (Material Constant, For GI=80, copper K=205, Aluminium K=126).
• Cross Section Area of Earthing Conductor (A) = (50000×1)/80
• Cross Section Area of GI Earthing Conductor (A) = 625 Sq.mm
• Allowance for Corrosion = 1.0 % Per Year & Number of Year before replacement say = 20 Years
• Total allowance = 20 x 1.0% = 20%
• Safety factor = 1.5
• Required Earthing Conductor size = Cross sectional area x Total allowance x Safety factor
• Required Earthing Conductor size = 1125 Sq.mm say 1200 Sq.mm
• Hence, Considered 1Nox12x100 mm GI Strip or 2Nox6 x 100 mm GI Strips
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