Friday, January 31, 2014

Calculation for Min. Cross section for Earthing conductor at particular fault level

Calculate Min. Cross Section area of Earthing Conductor

Cross Section Area of Earthing Conductor As per IS 3043 (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